noun. One who severely questions and cross-questions another; specifically, one who severely questions a candidate for the purpose of finding some weak point in his political creed or professions, or of bringing out his actual opinions or position.

noun. One who heckles or uses a heckle.

noun. Agent noun of heckle; one who heckles; somebody who insults, makes fun of, or teases.

noun. someone who tries to embarrass you with gibes and questions and objections

"By the way, the term heckler actually derives from the textile industry, but these guys are once again apparently out to redefine the term."