Here is the full list of all 12 Burger Butt achievements.
Unlock the bow skin!
Unlock the crown skin!
Unlock the cat ears!
Unlock the wizard's hat!
Unlock the classic Shit Storm skin!
It's Mega!
Unlock the cop hat!
Unlock the red cap!
Unlock the arrow hat!
Unlock the pirate hat!
Unlock the big brain hat!
Unlock the Santa hat!