When a man feigns an attempt at anal penetration in order to startle his partner.
Woman: I told you I don't do that!
Man: Don't worry, I'm just knocking on the back door.
The theory that people prefer the method in which their mom made tuna and potato salad over all other methods.
"I bought potato salad from the deli, but it's not like Mom used to make!" It just goes to show that The Tuna Fish & Potato Salad Theory is true.
When a woman, while engaged in doggy-style sex, reaches between her legs to fondle a man's balls.
Also see: playing quarterback
Guy 1: Man, I love it when my girlfriend is "playing center".
Guy 2: What the hell does that mean?
Guy 1: Look it up on Urban Dictionary.