In A.C.E it is Donghun
He constantly tells Jun how he would dislike and hate him and even says a lot mean things to the other members, altho it's mostly just joking and nothing to serious, but he really has that thing where he especially to Jun says a lot stuff like "I don't like you", "Why are you in my group?" , "Why are you even the leader?", "Just shut up!" , "Nobody likes you" etc.
Who is the most savage in your ulti group?