That expression is slang and very informal.
It's OK to use with your friends, but it doesn't sound nice.
It is not OK to use it in a professional, business or work situation.
1. rude slang To greatly anger or irritate someone. I think I might start cycling to work in the morning—this traffic really pisses me off! I think I pissed off Janet with my comment earlier.
2. rude slang To depart from somewhere quickly or abruptly. Often used as an imperative. Why don't you just piss off if you're not going to help us? I didn't know anyone at the party, so I pissed off around 11.
Very disgruntled, angry, or outraged. John was so pissed off when he found out that someone else had been given the promotion instead of him. There's no point in getting pissed off over a bad grade on your exam. Just study harder next time!
to piss someone off
Inf. to make someone angry. (Crude. Potentially offensive, even though it is widely used. Use with discretion.) She really pissed me off! That's enough to piss off anybody.
No! Pissed off means angry or annoyed or frustrated. It is very strong and informal. You do not use it simply because you are bored.
Example: If I drove one hour to meet someone and that person never even showed up, I'd be pissed off.
I think we may have a translation problem going on here. I suspect that when Julio says 'bored', he is mistranslating the Portuguese word aborrecido, which can actually mean 'annoyed'. In other words, Julio does know the meaning of the target phrase, but he's giving an inaccurate English translation of it.
As for p ****ed off, yes, it does means angry/irritated/annoyed, in both British and American English. It's widely used, but it is vulgar and sounds unpleasant.
I do use mildly vulgar language sometimes, but I never use that phrase. As Richard says, it is crude and potentially offensive. I agree that you should avoid it. It isn't a 'nice' expression.
I don't know what the phrasal verb to piss off means in British English, but the adjective pissed has a different meaning:
American English: He is pissed = He is angry.
British English: He is pissed = He is drunk.
young children = no
between co-workers (men only) = not nice but OK
older people = no
between teenagers = OK
between student and teacher = no
between friends = OK
5 year old = no never