These are some good ones. I hadn't checked this thread for a couple days. Here's another one the instructor uses when people get jerky and try to force a move to work:

-Fast isn't fast. Smooth is fast.

And some others:

-You say "It hurts when I try to do that/move like that/bend that way." Well, then don't do it that way.

-Don't think too hard about doing it right, because then you won't.

-If you screw up don't just stand there and stare at your opponent. Hit them and try something else!