British "pissed off" = very angry. American "pissed" = very angry. British "pissed" = very drunk.

all the other answers are correct, "pissed off" means angry in american english. a person "can be pissed off" he didnt get a raise, or "piss someone else off" by stealing their parking spot... etc. you get the idea. in Britain it can also be that "to piss off" means to "f**k off" rather rudely during an argument or "get away". for instance, an irritated young man may say "piss off" to a drug addict on the street pleading for money. or a woman may say it to unwanted attention from men to get them to leave her alone. . jokingly, young people sometimes say it to their friends, in a similar way as "f*** off!". (but im my opinion its a bit crude of language to use)

It means angry; it can be a verb or an adjective. Now the old joke - a rich, successful, handsome, happily married, healthy and strong man suddenly lost everything and in despair he called to God, "why me?" and God answered; "because you piss me off" (verb). You could say he was pissed off (adjective). It's not polite English but it's pretty common here in America. It's informal and I would not say that to my boss. Good Q.

the british use a lot more emphasis when they say it like they are really angry I think we americans say it more casually like an observation.

I think the British leave the ed off and the me