a Fergasun
A Fergasun happens when a guy posts something so dumb it makes everyone laugh, then he cuts and runs like he's being chased by a dragon.
A guy posts, "I believe the moon is made of cheese and also a conspiracy." Then he never logs in again.
Someone starts a thread about why socks are the most important invention, and then disappears.
A person says, "The internet is fake, and I'm the only one who knows." Then he leaves forever.