I think we are all guilty as charged in relation to this logical fallacy.
The tu quoque fallacy (pronunciation: tu-KWO-kway) occurs when one person accuses someone else with hypocrisy or inconsistency in order to avoid taking the other’s position seriously.
Father: You shouldn’t have cheated in your exam. Don’t you realise that’s wrong!
Son: That’s rich coming from you! You cheated on your exams when you were my age!
From the Latin “you too”, this is known as the ‘pot calling the kettle black’ or the ‘two wrongs’ fallacy and is a type of ad hominem because one person attacks the other.
In this example, the son commits the tu quoque fallacy.
He dismisses his father’s argument because he believes his father is speaking in a hypocritical manner. The son may be right in his counter-accusation, but that does not show that his father’s accusation is false and invalidate his argument.
Personal inconsistency in others is hard to stomach and can lead to ‘childish tit for tat’ exchanges but the moral character or past actions of your opponent are generally irrelevant to the validity of the argument.