Actually, I think in most cases, you could use "pissed" *or* "pissed off" in American English.
Another difference I see a lot--I hope I'm using it in the right context here. UK version: I have done, as in, "Have you done <whatever>? Yes, I have done." US version: I have, as in, "Have you done <whatever>? Yes, I have."
At least, I think that's the right context. There's definitely somewhere that I tend to see "have done" where I would drop the "done."
