the word order is always "piss you off" or "piss me off." Yes, "to be pissed off" means "to be angry," but keep in mind that this is a very rude phrase and should not be used lightly. If you ever saw this to someone, then you are expressing a stronger kind of anger.

"You really piss me off" is correct. You're really pissing me off (now, present continuous), He's really pissed her off (present perfect) etc. But be careful with this phrase as it's bad language that you would only use when you're around people you know well or those that you're not worried about offending with your words (because you're so angry!).