1
A stupid headbutt battle where friends or enemies crash into each other like meatballs in a sauce until one person finally flips out and quits. Usually happens for a few bucks on a dirt patch.
'I bet I can beat you in a pachycephali!' 'You're on, you idiot.'
They had to drag them off the field after that pachycephali match.
He only joined the pachycephali because he owed me five bucks.