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.