The tu quoque is a very common fallacious ad hominem argument in which the subject of a criticism attempts a defense by turning the argument back toward the original critic.
Since it is almost invariably irrelevant whether or not the critic is also guilty of the original criticism (usually not) this argument is a red herring. The tu quoque also commits the "two wrongs don't make a right" fallacy.
Theists seem to love tu quoque arguments:
"Richard Dawkins is a fundamentalist too."
"Atheism is a religion."
"Crimes have been committed in the name of atheism too – just look at Adolf Hitler and Joseph Stalin!"
"Science relies on faith too!"
Such tu quoque arguments are not only inaccurate, but they are also irrelevant to whatever point the theist is attempting, ineffectually, to make.