Break a Leg

I used to date a girl who was into theatrical arts.  Before one of her shows, I wished her good luck, and she got all annoyed with me and told me that I was supposed to tell her to break a leg.  I looked at her oddly and said, "Why would I tell you to do that? If you did that, then I'd have to drive you to the hospital, you'd miss your show, you'd have to walk around on crutches for a month, and I'd have to, like, take care of you and stuff.  If you want to play doctor, that's cool, but you d...