I've always imagined a situation after I saw the hentai of Ben 10 fucking Gwen (her cousin).

Ben starts fucking gwen and they were about to cum but the Omnitrix malfunctioned and Ben turned into Forearms (on of the alien avatars of ben) and Gwen just gets torn right from her pussy till her chest and her inners, drenched in cum, falling down. And ben is clueless of what happened.

(Forearms is giant alien and his dick probable would never fit any human girl)