During the act of masturbating in bed, when you are too lazy to ejaculate into a tissue or other alternatives, you ejaculate into your hand. You leave the semen in your hand until the morning until it is dry. Once you wake up you go to wash it off.
"Dude whats that you got in your hand?"
"Uh.. I was making a mayonaisse sandwich.."
"... You wilhemed again didnt you?"