To troll someone means to deliberately provoke or annoy them, usually by saying things you don't really mean just to get a reaction. When someone trolls online or in person, they're doing something similar: tossing out provocative comments to see who will “bite” and get upset.

Trolling differs from honest disagreement or good-natured teasing. A troll doesn't care about the truth or having a real conversation. They just want to stir up confusion or frustration for their own entertainment. Light trolling between friends who understand the joke can be playful, but trolling strangers or going too far crosses the line into cruelty.

The word troll is also a noun. “Don't feed the trolls” is common advice, meaning don't give trolls the attention and reaction they're seeking.