http://en.wikipedia.org/wiki/Tu_quoque
Tu quoque /tu?'kwo?kwi?/,[1] (Latin for "you, too" or "you, also") or the appeal to hypocrisy, is a logical fallacy that attempts to discredit the opponent's position by asserting the opponent's failure to act consistently in accordance with that position; it attempts to show that a criticism or objection applies equally to the person making it. This dismisses someone's point of view based on criticism of the person's inconsistency, and not the position presented,[2] whereas a person's inconsistency should not discredit their position. Thus, it is a form of the ad hominem argument.[3] To clarify, although the person being attacked might indeed be acting inconsistently or hypocritically, this does not invalidate his argument.