In Internet slang, a troll is a person who sows discord on the Internet by starting arguments or upsetting people, by posting inflammatory, extraneous, or off-topic messages in an online community.
http://www.ranker.com/list/top-reasons-why-someone-is-a-troll-online/stokified, internet, other,
Loser
Racists
Douchebag
Spoiler Troll
Hypocrites
Grammar Nazis
Sexists
Acting Like You Know Everything
Random Argument Troll That Doesn't Make Sense
Narcissist