Best use of a key/button in a game

[Medzy]

Name your favorite key (as well as its function) from a specific game
Whether it's the Ctrl "camp" key in CS:S; the Square "Damn, I'm lookin' good" button in Duke Nuke Forever; Press X to "JASON"; or my personal favorite:

The F key in Brutal Doom.

Spoiler: It's the "polite suggest to your enemies that they won't win" key

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[Jimbob]

Triangle in yakuza 4.
FEEL THE HEAT