Penny: Okay, this is about science. Why'd you come to me?
Sheldon: Well, because it's also about my reputation. And somehow you manage to hold your head high despite your checkered past.
Penny: Checkered past?
Sheldon: It's a figure of speech referring to how sexually promiscuous you were.
Penny: Really? Well, I've got a figure of speech about how sexually promiscuous you can go be with yourself.