Akin to moron. Is used to describe someone who is acting stupidly, or in a imbecile manner. Usually the use of the word is triggered by speech or an act of incredible idiocy; a feeling of cringe on the part of the accuser after witnessing the unfortunate/hilarious event is also common.
It's when a person is a combination of both chubby and buff. Like if a man has man boobs but he is totally ripped at the same time. That is what is called chuff.