Yeah, maybe I'm just going into old-fogey-hood, but I'd like to repeat a Reddit post from 3-4 years ago involving the definition I use for trolling. There are three core features:
1. Trolling always means the user is, in some way, not sincere or not honest in their interactions
Either they do not believe what they are saying, or else they are saying it only because they have an ulterior motive/goal which is not obvious or apparent.
No matter how moronic, argumentative, or misinformed a person might be, they cannot be a troll if they are trying to be honest and their motives are straightforward.
As you leave the context of internet forums and discussions, the words "sincere" and "honest" get trickier to apply. For example, if you are playing a strategy game, the enemy is not "trolling" when they trick you about what kind of army they are building, because that kind of thing doesn't represent a breach of trust..
2. Trolling is always about triggering or goading victims into a reaction
Causing injury or offense to another person is not--on its own--trolling. If a pickpocket steals your wallet and runs away, he did not "troll" you, because he doesn't care about how you react, he just wants to escape with your cash.
If a fast-food employee secretly spits in your hamburger, they are not "trolling" unless they expected you to notice...Or unless they start dropping little hints afterwards to prompt you for a reaction. Major asshole, yes, troll, no.
99% of the time the troll is seeking a reaction with an emotional component. "Negative" reactions such as rage, frustration, or annoyance are especially common.
Not-so-negative reactions can be used, but are less common. For example, an atheist troll might say encouraging things to make a fundamentalist-Christian community enter into a celebratory circle-jerk.
3. Trolling is not the same as humor, trolling can incorporate humor, but only in a "mean-spirited" way
Many people seem to get confused by this, since jokes and humor often fall under both #1 and #2 above, being attempts to use insincere words to cause an emotional reaction.
Trolls are never laughing "with" their victims. They are always laughing "at" their victims.
Trolls may sometimes try to get you to laugh, but if they do it is only because there is some "larger joke" which you are the butt of.
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Side-note: When people troll badly, I prefer not to call them trolls. This is sort of like how someone who burned a meal isn't "a cook". Sure, they technically did the "act of cooking", but it seems like calling them "a cook" wrongly implies that they are good at it.
Source: http://www.reddit.com/r/funny/comments/p7u3k/troll_level_mas...