Awesome word. The moral of this word is to blame the guy for same reason for which he blames you. If you did'nt get it then not to worry 'cause eventually you will . Well talking about etymology .... this word comes from Latin ( rather its a Latin term in itself) which means "you too". And its pronunciation goes like 'TOO-KWOH-kwee' (don't get it wrong:)anyway)
Dictionary meaning (noun) - a retort charging an adversary with being or doing what he or she criticizes in others
Example sentence -- If I resort to tu quoque against you will be convicted of the same sin you see in others.
Fun description -- Well you can use tu quoque for many useful retorts.
For example ...you may have your boss always nagging you to change your childhood idiosyncrasies ..... it's time to stand on your feat and make your boss realize that his idiosyncrasies is nothing godly either !! Just go and say -- ' you need to learn manners while you you tell me do the same' (get the essence)
When someone says you -- " hey man ! you need to change your suit coz..... " then without letting him finish just make a quick statement -- " hey... ain't you wearing that same blazer for past 6 months ? " . That's tu quoque !!
Then lets say the guy next to you with those familiar curled eyebrows says to you -- " Can't you keep your mouth shu...." then you just need to interrupt in between ( right timing rules :P) and reply " Shut up !! you ain't letting me concentrate " :P
Lastly it helps specially in debates .... 'cause even if you have no point to say .... you are always free to resort to tu qouques against your opponent :)
P.S. -- Before you tu quoque me let me quit the scene now !! :)