White water rafting
It's like motor boating a girls boobs except instead of moving your head side to side, you head butt her vigorously.
Example:
Girl 1: "Hey so how are you and Nate doing?"
Girl 2: "Oh last night he tried this new thing with me called white water rafting."
Girl 1: "Hey so how are you and Nate doing?"
Girl 2: "Oh last night he tried this new thing with me called white water rafting."