When a male is laying down on his back, and blows a load on his belly button. Girl dips her nipples in his belly button and then puts them in his mouth.
When someone is dating someone that is either too ugly, old, young, or just plain wrong for them. It can also be used when you're dating someone in a much lower socio-economic class or someone of a different race or level of intelligence.
Fred: Dude, so who're you into these days?
Tim: This freshman in high school. She's really cute.
Fred: Gross... you're a sophomore in college. Way to start dippin' in the fondue.
Katie: What do you think about me dating Joe?
Jen: Are you serious? He's so fugly. You'd be hardcore dippin' in the fondue.
The playmates who date Hugh Hefner
The late Anna Nicole Smith with her rich, old, crusty husband
Short-hand for the word floccinaucinihilipilification, meaning the estimation of something as valueless (encountered mainly as an example of one of the longest words in the English language).