When your head gets all tingly, an orgasm of the head.
Dude I totaly just had a headgasm after that head massage my girlfriend gave me.
An orgasm for your head delivered by a "Headgasm" scalp massager. Only the best feeling in the world. Comparable to the feeling of a cold shiver down your spine, but on the top of your head.
That thing is like an orgasm, for your head! Headgasm!