I dont feel like defining it, but reviewers make one.
I am thinking about someone on facebook who trolls on peoples statuses
troll 1307 up, 167 down
One who posts a deliberately provocative message to a newsgroup or message board with the intention of causing maximum disruption and argument.
A person who, on a message forum of some type, attacks and flames other members of the forum for any of a number of reasons such as rank, previous disagreements, sex, status, ect.
A troll usually flames threads without staying on topic, unlike a "Flamer" who flames a thread because he/she disagrees with the content of the thread.
Example: Someone on facebook who hates on every status I post, is a status troll