I was in a group where someone said this. I find it funny, because if a mob is on you you're "tanking" it. Just because you may be ill-equipped for it doesn't mean for a brief moment you're weren't performing the role.
I think quite often people forget how hard things hit because they aren't usually the ones getting hit.
I secretly like when someone pulls something off one of my tanks and summarily see their health drop. The player usually watches their aggro the rest of the run.
Playing the game wrong
19 hours ago