Russian roulette

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A stunt in which one spins the cylinder of a revolver loaded with only one bullet, aims the muzzle at one's head, and pulls the trigger.
• noun An act of reckless bravado.

from the GNU version of the Collaborative International Dictionary of English.

• (Fig.), (Fig.) An act of bravado played by loading one bullet into one chamber of a revolver in which the cylinder has five or six positions, spinning the cylinder (thus moving the bullet randomly to one of the six positions of the cylinder), pointing the gun to one's head, and pulling the trigger. If the bullet is in firing position, the "player" is usually killed. Such a "game" may be played on a dare, or, in some places, as part of a gamble.
• Any dangerous act resembling Russian roulette in the acceptance of a high risk of serious negative consequences, usually unnecessarily.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• proper noun idiomatic, games A deadly game in which a person loads a single bullet in the cylinder of a revolver, spins the cylinder so that the location of the bullet is unknown, points the weapon at his/her head, and pulls the trigger. In its most lethal form, played by multiple participants each of whom takes a turn until the weapon discharges.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a stunt in which you spin the cylinder of a revolver that is loaded with only one bullet and then point the muzzle at your head and pull the trigger