when a bullet fired from a gun strikes its target at a funny angle, the resulting asymmetrical hole looks like a keyhole, hence the name. usually caused by a worn or damaged barrel, or poor quality/incorrect caliber ammunition.
that ancient pistol i inherited from my grandfather is so worn out, half the time the bullets will keyhole and the other half of the time i can't even hit the target.
Town drunk of Sauk Prairie. Do not headbutt or you will be injured. Has been known to "keyhole" a beer in .85 seconds and did a keg stand of 4 minutes and 20 seconds. Has retarded people assist him rolling joints. He had to wear a 40 lb. vest in jail.