perfidy

The bleachers at Fenway Park. Boston's renowned xenophobia and proviciality plus the Red Sox Nation's Napoleon complex and belligerent self-flagellating anger, both in concentrated form and augmented by beer, and all focused on anyone or anything who doesn't wear a red "B" and hoot.

Runner up: I wouldn't want to be a Pittsburgh fan wearing the gold and black in Cleveland Stadium on a day when the Browns get beat hard by the Steelers.

Second runner up: Townie bars in Gloucester, MA. "Hey buddy, you from around heah? You from around heah?"

Americans traveling in any other country.

OK, I can second BRGDT's too. Although in Europe, the big hate is on for Dutch tourists.

The Dutch!

"universally ambivalent to your continued existence?" - that's easy. Manhattan. And Paris.

Rudest "people experience"? French-Canadians. (Ross doesn't belong in this sub-species, does he? If so, please delete this comment, as I do not need Ross pissed at me) Worse than the French, with none of the down-home goodness of the normal Canadians, and snooty for no damned good reason at all. At least the French have centuries of history, countless surrenders, runny cheese, and indifferent hygeine about which to be snooty. Not all of those are universally deemed good, by the way, but, hey, they apparently work for the French, though not the French Canadians.

For reference, I'm from south Texas, a place I'd been told was full of pushy cowboy types, rude as the day is long. Not so - they're almost unfailingly polite but situationally boneheaded, like most of the rest of humanity, including me.

Patton, funny, what you say about Texans, I have found to be true about Manhattanites. Sure, they have as a matter of daily gettin' by all developed an eff-you shell, but I find New Yorkers, simply by dint of the fact that there are so many of them in so little space, are pretty respectful of what little personal space you have, helpful, and perfectly willing to lend a hand.

Just don't make eye contact with anyone... they'll think you're going for their wallet.

Patton,
I don't know if Ft Hood and environs (Bell County, Coryell County) count as "south Texas", but most of the people I came across there were astonishingly polite. So much so that I started to build extra time in my schedule. I knew that I would have to engage in conversation with whoever was running the Diamond Shamrock when I went in for gas and smokes and planned accordingly.

The single rudest person I ever encountered was the Pakistani (?) guy working the long term parking lot at LaGuardia one time.. I flubbed the transaction, and mistakenly re-submitted the credit card into the machine to pay for the parking...the guy went off, in his thick accent, "WHY YOU PUT IN CARD AGAIN?! WHY YOU CAN'T READ THE FUCKING SCREEN?! READ THE FUCKING SCREEN!!" etc etc

Actually, he was also the funniest guy I ever encountered- my friend and I were in tears hearing him rant.

And PS- I acknowledge the French-Canadian side of my bloodline, but rarely speak to relatives from that side. It's better that way, non?

Oui, et moi faites des excuses pour n'importe quelle offense.

Ah, rude people. Where do I start?

There are those who are knowingly rude and arrogant, then those who are unintentionally rude.

For me, that would be Manhattan socialites. Whether it be looking one person up and down or mocking their attire or flat out not even saying hello.

Yuh, whatevah, beeatch!

Patton,
If that means something like "No offense", which is as close as babelfish seems to render, none taken. My heart is harder than a stone wall...but one built by Robert Frost, so it's a bit soft at the center.

And Ross- he's made of sterner stuff than runny cheese.

GL,
Good topic. As a western MA transplant to Boston, I have to agree with Johno's comments and overall Boston assholedom. And I do find residents of NYC much more helpful than the rude stereotype they carry (they seem to appreciate the hassle Manhattan presents to a visitor, as most you encounter aren't original New Yorkers themselves). And though I agree that Southerners overall tend to be outwardly polite, I find that their rudeness tends to come after the person turns their back, or its more of a deflective F.U. instead of having it immediately spit back at you (it kinda seeps in later - wow - that condescending prick was actually really rude to me).

My personal favorite - after experiencing a smile-filled week in Georgia, I flew back into Logan Airport. Before I even left the airport, I had the clerk at Dunkin Donuts give me shit about my coffee order "you can't order an iced dunkachino, you STUPID FUCK", and had the parking attendant try to screw me out of my change. I was home.

General multiple rudenesses from the general population... as opposed to particular rude persons in a population:
Paris. I was last in France in the 70's. They've despised Americans for a long, long time and they are rude about it.
Rome also has its points. Most other rudeness I've run into seems to be specific rude people or cultural misunderstandings.
Oh, for another generally rude group. Tourists. Any nationality, anywhere, you tend to find a very very high percentage of rude people. I try not to be a rude tourist (except I slip sometimes and get rude at other tourists...).

If you aren't a jerk from the get go most people will treat you with respect or at least benign indifference. Manhattanites will talk to you, even in bars. Try that in DC. The folks in Gloucester, MA bars were nice the night I barhopped there. Small town, we might have hit them all. The rudest could-give-a-shit about you people I have ever met are in DC at events where there is a ladder that is perceived to be climbable. But those few people are assholes anyway, so who cares?

General ambivalence towards my continued existance? Standing in a long lineup at any government office - the worst being the Registrar's Office at university(not so much for special rudeness as for the length of the line - it streams out of the building, which is impressive as hell considering that the office is on the second floor). You can tell when people just don't give a fuck about their jobs, and that's the best place to find it.