Slang for a hand gun. Best used in Mickey Spillane-type crime novels.
....just so the broad knew I meant business, I decided to introduce her to my best friend; a hand-puppet I liked to call "Mr. Thrity-Eight"....
When a person commits suicide by blowing out their brains with a gun, the residule of blood/brains splatter on the wall in a shape that resembles a flower.
Kurt put the gun to his mouth, pulled the trigger, and painted a wall flower across the bathroom mirror and shower stall.