In MMO games tanks are the characters that are supposed to take most of the damage, unless... they are french. In that case the word has two definitions either:
A tanking character that is acting like, a little sissy and entering combat last.
A caster or other low-hp character that is acting like a tank for no good reason and overall fucking up everybody's game.
French tanks can be seen mostly in MMOs like: WoW, LoL, HoN,DotA and the such.
"Why is Rammus backing out?!?!"
"F*ck.... we got a french tank"
"Ok, once they are in range Alistar is gonna stun'em and then... Wait, wait Ryze wtf u doing man?!?!"
"He frenched tanked them...."