The distinct area off the bottom that is at the lower part of the gluteus maximus. Usually the underbutt is highly regarded in terms of attractiveness. Often the underbutt is discovered at the beach when womens bikinis do not cover the whole area of the bottom.
when a man leaves too many buttons undone so chest hair is sticking out
alberto: what do you think, am i under buttoned?
rosita: you could make a wig with all the chest hair i can see - when not wearing a tie, two buttons or more is underbuttoned
Someone that just can't seem to do anythingright. So much so that everything they touch turns to shit. See also clod or dimwit.
Byron: Everything he touches just falls apart. It's almost like the poor dolt is cursed.
Tobias: yup. He's a dunderbunny like you read about. Stupid hamfist!