A person, oftentimes a young male, who whines incessently too the point of driving those around them crazy. Oftentimes the whining is accompanied by extreme stubbornness and a refusal to admit when one is wrong.
Ex. The buttchuck refused to do his homework, instead, for ten minutes he listed all of the reasons he shoudn't.
The ultimate insult you could bestow upon anyone who talks bullshit all the time. as a double whammy this word also means the explosive matter that could come out of the ass at such great speeds that it seems like your arse has been out drinkin to much last night.
Person 1: So I saved the entire population of Ireland with a string and a folk!
Person 2: Bullshit you did you buttchuck!
Man I had the biggest buttchuckin session last night!