When during fellatio, after ejaculation, the female (or male) performing the fellatio punches the recipient directly in the testicles. This therefore turns the recipient's testicles purple giving them the look of purple plums.
Dude I was getting head from this smoking hot girl last night...and then she gave me a purple plum knocker. My balls haven't been the same since.
by Funnyudwords April 20, 2013