Lat.: "you too!". A form of rhetorical distraction technique (red herring) in which, instead of countering an argument, the person making an argument is attacked (ad hominem) by being accused of holding or having held in the past a different position, or of having behaved inconsistent with the position.
A: Why do you still drive such a fat SUV? They only pollute the environment!
B: And you fly to the Seychelles twice a year for vacation. That's at least as bad!
Although it is questionable under these circumstances for A to play the upholder of moral standards, B’s reply does nothing to answer the question of whether or not it is justifyable with regard to the environment to own and drive oversized vehicles.
The tu quoque-argument is very similar to whataboutism, the difference being that it specifically unfairly attacks the opponent personally and thus is a form of ad hominem-argument.
This is one of the most common unfair attacks in discussions, likely because it is both quite effective in diverting the discussion away from the actual topic and also because it is relatively difficult to counter.
As used here, this is a form of an “performative ad hominem”, i.e. a personal attack based on denying the opponent the right to use a certain argument.