The fact is, the A's have to share a market with the Giants, who are the region's media darlings (especially a well-known cheater by the name of Bonds, Barry), while the A's are relegated to being on the "backburner". This generates resentment from us A's fans. This is not something that can be applied to the Steelers/Eagles situation, where each team has their own primary market.

As for why rivalry/hatred between fans exists in a more general sense, you have to realize it all boils down to the fact that team sports are a stand-in for intertribal warfare in this day and age.

Barry Bonds

Otherwise I don't hate the Giants at all.

They got swept in the bay bridge series, I can still talk crap to my friends since they have never won a world series in SF. Will Clark was the man too.

i dunno. But I didn't hate them so much when they were at candlestick, and maybe it's cuz of the fans that adopted them once they moved to "phone company" ballpark. I've literally seen tailgate parties with tablecloths, wine, wine glasses, cheese, baguettes...all well and good at an Italian restaurant, but a wine and cheese tailgate?
The Bonds era definitely creates a media frenzy that helps bury our wonderful Athletics in the news, and I think we all resent that. The A's should always be the first story on the sports segments, especially last year, with Bonds out and the A's making such a furious comeback...wasn't always the case though. In fact, almost never were they first on the news.

Although he's a big part of it. It's how the organization has pandered to him and covered up his dirty laundry for years, even though he treats his own team and management with contempt. The message is: No matter how awful you are as a person, and how badly you treat other people, it's all forgiven if you can hit lots of homeruns. Not a good message. And Giants fans treat him like a hero.

That being said, I have to admit there's one Giants fan I love: Grant, over at McCovey Chronicles. With all respect to Blez and Nico and others here, he is hands down the cleverest, funniest, and most inspired sports blogger around.

Sort of like the Brooklyn Dodgers, or the Red Sox until recently (sigh), they are usually pretty good (well--ignore late 70s and mid 80s, heh heh), but always seem to just fall short.  No better example exists than the '02 series, when they got complacent only 8 outs from victory.  As a baseball fan, you have to appreciate the agonizing trip they've put their fans through for the past, oh, 47 years.  
Now myself, as a Bay Area baseball fan, I love having two teams, one in each league, to watch.  I am definitely an A's fan, no question about it, cuz I'm an East Bay guy, and besides, I started following the A's in 1980 right when Rickey exploded into being the most exciting player I've ever seen.  But I do like being able to listen to two ballgames in one day, especially if the A's are off on the East Coast and the Giants are at home, or vice versa.  I can put up with their "homer" announcers, and besides Jon Miller is damn good.  Following the Giants keeps me in touch with the National League and the big picture as a whole.  
And as others have mentioned on this thread, the Giants are very much the opposite of the A's; load up on veterans again and again (I mean, they're excited about adding 40-year old Steve Finley to their average 40-year old outfield?  Who are they kidding?), don't have a lot of young talent, do have a great ballpark (now that's one I do wish the A's could emulate), and do seem to have more cell phone yapping yuppy fans--at least since they moved from Candlestick.
So no hate here, just an appreciation of the Giants' tragic course through baseball history.  Oh, did I mention the 1989 Series yet?  Tee hee!

1. Giants get the lion's share of the local media attention, regardless of how they're doing.  Not much can be done about that because there's really only one big sports radio station in the Bay Area (KNBR/Ticket1050).  Meanwhile, the A's wander from station to station every couple years (in the last decade or so, I seem to remember 560/610/910)
2. Ever since they moved to Canyouhearmenowlookiti'montv-Park, they've attracted 'fans' that go for the status symbol instead of being actual baseball fans.  Casual fans wouldn't be that big of a problem except they've really got sloppy fan etiquette (cell phones, laptops?!?!, etc)  Then again, larger A's crowds have been known to do the wave ... while our own pitcher is pitching.
3.  Giants fans talk a lot of smack for a team that has never brought a World Series trophy to the Bay Area.
4.  In most two-team regions in most sports, it's nearly impossible to truly be a fan of two teams, whether it's 49ers/Raiders, Cal/stanfurd, UCLA/U$C, Lakers/Clippers, Dodgers/Angels, Cubs/ChiSox, Yankees/Mets, etc ... In most pairings, there's often geographic and perceived demographic differences ... goldenchild/blacksheep, whitecollar/bluecollar ... Since sports fans tend to identify themselves with a group, it's only natural that they pick one or the other.

you probably wouldn't ask this question. People who live in the bay area know why they hate the Giants and their fans.

Basically if you are an A's fan in the bay area all you here about it is the Giants and it sickens all of us especially since they have never won a World Series since moving here from NY.

Their fans are came out of no where in or around 2001 and a lot of them have no idea about their team or team history. They are bandwagoneers.In 1999 or 200 when they were in Candlestick nobody gave a crap about the Giants they were boring.

I hate the Giants.  

My biggest problem with them is with the "territorial rights" they have to the South Bay.  It bugs me to no end.

1.  If the A's were to move to San Jose, it would actually move them FARTHER AWAY from the Giants than they are now.
2. The territorial rights granted to the Giants were so that they could move to San Jose instead of being moved out of state to Tampa Bay.  Well, this is a moot point now as the Giants got a new stadium in San Francisco.
3. Not only is the stadium issue for the giants a moot point, but, the election in San Jose FAILED.  They didn't want to pay for the Giants stadium.  And not only did the San Jose election fail, but, an election in Santa Clara failed as well.

So, basically at this point, they are holding the area hostage despite the fact that they don't need it and that twice in elections, the area refused to pay for stadiums for them.

And what ticks me off also, is that, the A's never went out of their way to try and make the Giants leave town back in the 80's and early 90's.  They never came out and said, as McGowan has, that the A's would have been better off without the Giants.  They never quoted market surveys as to how much revenue the A's would have lost from the South Bay market if the Giants had moved there.  But, that is what the Giants are doing.

I never laughed so hard as I did when Glaus hit that 2 run double to take the lead in Game 6.  He is my lifelong hero.

that I hate the Gnats is/are Kurkow and Kuiper. Especially Krukow. I cant stand that guy. He is the biggest homer that I've ever heard and he is a freaking dork with all of his little catch phrases. He even has a commercial here in Monterey for some golf shop and he's annoying as hell in that too. I'm starting to see Tom Tolbert mutate into Krukow part two.

The Giants are my second favorite team, and I'm quite a Bonds fan.  There's no one I'd rather watch bat.

I'd say there's less of a rivalry between the A's and Giants relative to the other intra-market rivalries (NYC, CHI, LA).  It also seems that A's fans care a lot more about the Giants than vice versa (which is also true of the White Sox, Mets, and Angels fans with ther respective rivals).  I guess it's natural as the second fiddle in media coverage...

and that scares the Giants, they think were idiots and losers while the Giants are like IBM to our DELL or Microsoft .

They just flat out don't respect our philosophy, our colors, our players, but they think we should bow down to all their old decrepid players they wheel out there.

Giants are Ginats like Goliath while the A's play the role of David constantly slaying the giant.

I loved it when we beat the snot out of them last year 16-0. I went with this guy who is a giants fan and he left after the third inning, almost all of the giats fans did. It was awesome.

I don't have anything against the Giants, except for the media bias.  That drives me crazy.  My sister says I'm being paranoid, but I swear, the Giants always get the front page story in the Bee while the A's articles (from the wire) are buried on page 5.  Plus, the Bonds factor.  They're always a bigger story.  
And yeah, KMAX drives me crazy, but if I take off my green and gold glasses, I can't blame them for carrying more Giants games if they get higher ratings here.  :-/

I think a lot of the dislike is caused by fans.  I'm not surrounded by many Giants (or even baseball) fans on a daily basis, so there's not much "rubbing it in their/our faces" going on.  I guess if I lived in the Bay Area or had to listen to a lot of B.S. from Giants fans every day, it would be different, but I haven't experienced it.  

And I don't get any pleasure rooting against the Giants.  I get a certain sense of satisfaction watching the Yankees, Red Sox, and Angels lose, but I don't get that while watching the Giants games.  <Shrugs>
And I do watch/listen to a lot of Giants games.  I just don't root against them.  

f'n Boston

That's my reason.  I'm remember Willie Mays playing, so I liked the Giants as a kid.  Candlesuck sucked with the lame chain link fence in the outfield ha ha.

The ballpark is sweet, I give them that, but the seats stink in the upper decks.  Best to get a cheap ticket to anywhere, and when the As or anyone else is spanking them, move down to the lower level (very very nice angle and view to the seating) when the Suppies (San Francisco Yuppies) leave in their high-pitched impotent white rage to prance home to gnocchi and a rerun of Will & Grace.

Back to the city.  SF is a sh*t city with a few diamonds and pearls mixed in.  But it's mostly ugly, rude, aggressive and hard-nosed (compared murder rates between SF and Oaktown in recent years?), yet obnoxiously, hypocritically and uncomprehendingly self-satisfied.  It's decadent, meaning it is failing and fading, not continuing or improving.  Walk the downtown and you'll fall over from the stench of a failing sewer and drainage system.  The streets are besotted with failed idealists (also known as panhandlers and drunks) whose vision was too bizarre even for the patent-leather shoe, spritzer-sipping, piss-Christ-viewing crowd of imported Eastern liberal school grads who squat on their haunches reading free weekly papers trying to find a bed-sit on their waitress-at-the-Stinking-Rose-with-a-side-job-as-a-nude-model-for-night-school-art-student salaries.

And remember, aged AN readers, even the Grateful Dead preferred Oakland for their New Years Eve concerts.

Once you're done dragging yourself up Snob Hill or crab-walking through Castro, ain't no other place in town to hear an articulate sentence or tri-syllable words.

Even Chinatown (really the best place in the city) pales in comparison to Oakland's Asian gourmet cooks.

The best thing about "Frisco" (who cares who gets mad about that name?) is its ideal and what it represents to people who flee worse in the USA.  The worst thing is the city's reality and the generations of Okie bums and losers who screwed and continue to screw it up.

Reputation be d*mned -- the East Bay is a far better place to be, from climate to a healthy mix of ethnicities to -- need I say it -- better baseball.  That's a secret, and it ain't dirty.  You gotta wonder, would it be better or worse if the secret got let out?

and been an A's fan for my entire life, my 2nd fav team if i had one would be the Giants. It's only when the A's play the giants when I start to dislike them, I can't stand losing to the Giants, other then that I always rout for them. and If the A's ever moved I would be a giants fan as quick as you can say jimmy jam.

you have no sense of loyalty.

If the A's moved i would still root for them. it would hurt me a lot since it is the only team i root for but i love them to death and couldn't see myself rooting for any other team especially not the Giants.

I will be a fan no matter where they move to,Fremont, San Jose, Vegas ,or Mars.

To all you who do not despise the Giants: if the A's leave the Bay Area because the Giants evoke some territorial right to keep the A's from moving to the South Bay (which by the way is further from San Francisco than Oakland) I bet your feelings would change drastically. And it's not at all a stretch of the imagination to beleive that the Giants actively would like their local competition to leave the area.