The devious but non-harmful tricks played on other internet users or MMO players. Usually preformed by griefers or trolls, but sometimes by just people in good taste. More complex ones may be done by script kiddies.
(In a game of tf2)
Player 1: Why does our entire team consist of sandvich heavies?
Player 2: :3
Player 1: Enough of this catfacery.
*You see stranger's feed as a copy of yourself*
You: -_- *nexted*