The worst kind of Douche bag there is. A "Done That" pretends like he knows everything about everything hence the (Done That) but will also agree with whatever you say. Most "Done That's" are actually retarded but have surrounded themselves with other retarded people so nobody has ever actually discovered it. Done That's have been know to molest their sisters and therefor continue the line of Done That's.
Harry: I fucking hate this guy, he always talks and talks and has no idea what he is even talking about!
Jeff: I know, he's a fucking Done That. I heard he fucked his sister too.