A trouble-seeking, aggressive person, who can -and does- turn any social situation into an argument, and, subsequently, a fight. Used as an adjective or a
noun -for stereotyping purposes- this word could apply to any
potential troublemaker.
Sometimes the term is applied to people who purposefully pick on other people seeking for a violent reaction, and the term could be exchanged with the word bully.
That dude is a
hell raiser, he just stepped into the
bar, started picking on random dudes and suddenly there was a massive fight going on.