I think the uke from hell is basically the opposite and is not committed to any attack. Like the uke who is supposed to punch you in the face but always stops the punch before it gets to you. If I tell you to punch me in the face then punch me in the face...it's my fault if I don't move my face and get hit.
Agreed, uncommitted attacks are not attacks, they are a defense to having to accept the "badness" of being the attacker in class, which means the "Ouchie," or "Whomp," or whatever the appropriate sound effect which happens when the technique is delivered happens to be. Also agree with Phy Truong that the person who takes things up a notch when that's not the lesson can be a real pain. Beginner trying to figure out where to move, and the other guy makes them pay with pain for every incorrect movement. Not good. Those folks need to train with someone like themselves, and they can go off and fight MMA or whatever.