butt up

bust one's butt

To work exceptionally hard.

butt heads

To argue uncompromisingly.

butt in

To join a conversation or situation in which one is not welcome or invited; to interject (connotes a rude or discourteous interruption).

full butt

headfirst with full force

get one's butt somewhere

Go somewhere, especially quickly.

kick butt

To be impressive; to be decisively good or pleasant.

show one's butt

To misbehave or act defiantly.