It's what ghetto/ignorant/beligerant (*mostly*) black and hispanic people do when they get angry. Commonly occurs while riding NYC public transportation, especially in the outer boros (e.g. The Bronx). This usually entails the chimpouter using skewed logic, racist comments, and extremley foul and almost intelligible language (or is it called ebonics?, I dunno).
Yo why this white b***h be talking shit? Damn (they all chime in) now wez gotz to be chimpn' out fo real son. Yeah dog chimpout time, that's whats up.