Tu Quoque

The logical fallacy, Tu Quoque. Tu Quoque is Latin translated as you, also or you're another. The modern vernacular would be "back at you" or at the grade school level "he who smelt it, dealt it". Person X accuses Y of action A. Rather than dealing with whether action A is true or not, Y turns around and accuses X also of action A. It is basically a diversionary tactic that is immensely effective for rhetorical purposes but completely irrelevant in terms of the question "Did Y commit action A".

An explanation from Fallacy Files.

Tu Quoque is a very common fallacy in which one attempts to defend oneself or another from criticism by turning the critique back against the accuser. This is a classic Red Herring since whether the accuser is guilty of the same, or a similar, wrong is irrelevant to the truth of the original charge. However, as a diversionary tactic, Tu Quoque can be very effective, since the accuser is put on the defensive, and frequently feels compelled to defend against the accusation.