Bet you never even knew chickens had buttocks! The 'buttock' in question here is an inaccurate translation of 'batak,' which is a chicken (or any fowl) leg. If you don't like smoked chicken buttocks, you can perhaps order an Uno Burger with 'union' and mustard or a smoked 'ramsteak.' I've had lamb and mutton, but never 'ram'... :)
All joking aside, Grill Uno makes delicious hamburgers and grilled meat sandwiches, no matter what they're called, with all kinds of toppings, and they're open 24-7!