The sexual act in which a man penetrates a woman's (or man's) navel, also known as the belly button, with his phallus.
1. Guy 1: Dude, I totally nerfelled that chick last night!
Guy 2: Sweet...
2. Betty didn't want to have sex with Tom, so instead she suggested that they nerfel.
3. James walked in on his dad nerfelling his mom last night.