Someone who purposefully tries (and typically succeeds) to make a conversation or group activity more difficult than necessary through (failed) humor or an abrasive personality.

Or

A person possessing false knowledge or lacking in crucial common sense with an obnoxious air of superiority and is incorrect

Alternative forms of the word are “chawchbag” and “chawch-hole”

Synonyms: ignorant brat, lowbrow petty, obnoxious witch

Invented in Borat's movie. It is said, when something great happens.