There's a plot. When taking a woman from behind, a man can really excite a woman by giving her a gentle slap on the butt. Nurses suck patients cocks. Men always pull out. When your girlfriend busts you getting head from her best friend, she'll only be momentarily pissed off before fucking the both of you.
Assholes are clean.
A man ejaculating on a woman's butt is a satisfying result for all parties concerned. Women always look pleasantly suprised when the open a man's trousers and find a cock there. Men don't have to beg. When standing during a blowjob, a man will always place one hand firmly on the back of the kneeling woman's head and the other proudly on his hip.