We've all heard someone say, "Do as I say, not as I do." Well, if we were to assume this advice was wrong simply because the person giving the advice wasn't following that same advice, we would be faulty in our logic. We've also seen (used?) the logic that, "Well Richard did it, too, and he didn't get in trouble? Why are you going after me about it?" People who use the tu quoque fallacy seek to justify their infraction of the rules by pointing out that someone else has done the same thing and gotten away with it. Perhaps, this is true, but that claim is completely irrelevant. The only issue to be concerned with is the guilt or innocense of the alleged wrongdoer in this specific instance.
Example: "Officer, I'm pretty sure I saw you speeding yesterday; therefore, it can't be a crime."
(What may or may not have happened yesterday really has no bearing on this current issue.)
Example: "I don't believe my friend, Bob, when he says that smoking is bad for me. He's a smoker, so he clearly doesn't know what he's talking about."
(Bob might, in fact, have something sensible to say about the perils of smoking.)
Example: "How could you call a foul on me? They've been fouling me just like that all game, and you didn't call a foul on them!"
Tu Quoque Overview