Tasha: Tell everyone I say hi!
Bryan: I don't think I will do that.
Tasha: Your a butt head!
Bryan: I don't think I am.
Tasha: you won't tell everyone I said hi! That constitutes as butt headedness!
It is is a different way of saying "You have to be kidding me!"
Only cool people can say this. If your not cool then your literaly saying you have to be poking my butt.
Hencing that you like being poked in the butt.