Is "pissed off" foul language?

"Pissed off" is slang, and is bad language, but not anywhere near as bad as the F word. It is becoming more acceptable today, but still should not be used anywhere where you're trying to make a good impression, eg in front of a boss/teacher/elderly relative.

In the UK, it can mean one of two things:
1. angry - "He looks really pissed off"

2. left (went away) - "He pissed off over there somewhere"

The word "pissed" on it's own can also mean two things here: 
1. drunk - "He was really pissed"

2. urinated - "He pissed against that wall".

I agree with the answers.  Anybody uses the F*$%K, has no ediquite or self control in how they write.  It is not necessary to express that way for any reasons.  Using the word 'pissed off' is as safe as you can get.  I hope my two cents worth helped.

yes, it is foul language