When two men are going to town on a womans boobs and they get so carried away that they accidentally headbutt each other.
A North Carolina Headbutt is a good thing.
Guy 1: Dude, me and a buddy were motorboating Courtney so good last night that we did the North Carolina Headbutt.
Guy 2: You motorboated on Courtney?
Guy 1: Who hasn't?
Guy 2: True dat.