While having sex with a girl, before you ejaculate you pull your dick out and ejaculate into her eyes. While she is unable to see you, you put hand cuffs on her feet to restrict her movement, then run away. Her blind restrictive movements will resemble those of a zombie.
Dude 1: Dude last night I had zombie sex, she wasn't happy at all, I left her like that and walked out of her apartment.
Dude 2: dude now she's just your zombie ex XD.