The tu quoque fallacy occurs when an arguer uses someone's hypocrisy to dismiss the claim which is the subject of that hypocrisy. It overlooks that claims may be true even if someone stating them is hypocritical in regard to that very claim.

Here is an example:

"My doctor said smoking is bad for me, but that must be wrong, because the other day I spied her in the parking lot, having a smoke herself."

That problem here is that the doctor's failure to follow her own advice does not mean the advice is inaccurate.