The practice predates the invention of condoms and was messy as the female's stomach was sprayed with sperm.
Kid K, popping up beside of the bed: "HEY GUYS! What are y'all doing? I wanna play, too!"
Husband to Kid K: "Get out of here! No you can't play with us but if you get out, I'll be out there in just a minute!"
Wife: "Crap... Another orgasm foiled by our little 'coitus interruptus'..."
"I dont know, go ask him."
"i cant, hes banging his gf"
"Guess you'll just have to go Coitus interruptus them"