[Flibb]

Wrestlers. They spazz out and give up when they are gassed, swept or about to get submittted.
Fat/big guys who use stuff they can just use against smaller guys and never against guys their size and strenght.
Women. They are usually so weak that you have to use absolutely no power at all and I haven't met a woman yet which was more technical than I am, so I have to either open myself up so much that they learn something or use techniques I usually wouldn't consider, usually something stupid or fancy.