Popular expression seen spouted by various 31337 h4xx0rZ of Ultima Online, aimed at lame newbs.
The term originates from the fact, at least in pre-Rennaisance UO, hitting tab toggled your combat mode/peace mode, meaning that if you hit it while in peace mode, you would go into combat mode to initiate combat, and vice-versa. So, naturally, hitting it three times from peace mode will get you into combat mode. Double clicking the 31337 h4xx0rZ would have initiated combat with him, and if he were in the city, the guards would be called in with a flash of lightning -
Thou wilt regret thine actions, swine!
and the h4xx0rZ would have looting and laughing rights to the victim's corpse. Outside of town, the 31337 h4xx0rZ would have been able to kill and loot the lame newb without fear of a murder count or karma loss.
If anybody offers you "god mode" in any game, whether it be by pressing Alt-F4, F12, or whatever easter egg-esque keys the makers may have put into the game, check your key bindings to be sure this key is not bound to "quit". | 
