The
art of deliberately, cleverly, and secretly pissing people off, usually via the
internet, using dialogue. Trolling does not mean just making rude remarks: Shouting swear words at someone doesn't count as trolling; it's just flaming, and isn't funny. Spam isn't trolling either; it pisses people off, but it's lame.
The most essential part of trolling is convincing your victim that either a) truly believe in what you are saying, no matter how outrageous, or b) give your victim malicious instructions, under the guise of help.
Trolling requires deceiving; any trolling that doesn't involve deceiving someone isn't trolling at all; it's just stupid. As such, your victim must not know that you are trolling; if he does, you are an unsuccessful troll.