Official in-joke explanation no1

Heheh: type of cackle-ey/chuckle-ey laughter to indicate oneupmanship over oneself or someone else. The joke lies in the fact that you can use it when you've done something stupid/you are a moron.

Eg: Me and Sam are currently luxuriating in a warm bath of moron with frothy bubbles of in-joke stupidity..heheheh.