The floorboards are weakest where they 'butt' (against each other). [=where they meet, where the ends of the boards touch each other]
As a child, she was a clumsy girl who was the 'butt of' everyone's jokes. [=people made jokes about her because she was clumsy]
Why don't you 'get off your butt' and do something? [=why don't you stop being so lazy and do something?]
(..) -Golly bob howdy! That's me! We're all up here! Hey, Chuckles, lookin' good. Yeah, she really got your smile. What the... l told you kids! Stay out of my butt! But soft, what light through yonder window breaks? Romeo, o Romeo, wherefore art thou Romeo? Next season, we're doing . (..)2010 Toy Story 3