The proper word for that part of our anatomy is arse, or bum or, in polite society, bottom!
'Butt' is a measly-mouthed substitute creeping more and more into our language.
I mean, "Get up off your arse you lazy scum-bag!" (When addressing your DH.)
Or, "Get up off your bum you lazy scum-bag"
Or, "Get up off your butt you lazy scum-bag!"
Which has the greater impact?
The last is a complete cop-out, folks - and we should object to it every time we hear it or see it!