What is Head Party?
1.
After you get really intoxicated on your substance of choice, be it
'Duuuuuude I am WASTED - let's start the head party!'
'Fuuuck me mate! Get some munchies and let's head party'
See
2.
when one girl is with a group of five or so guys and gives them all head one by one.
"dude, i heard shannen had a head party last night!"
See