What do you do when someone gives you a bone-crushing handshake?

I think that sometimes a weak handshake can indicate that someone is timid, lethargic, or lacking in enthusiasm, but it can also be caused by arthritis. So when someone gives me a weak handshake, I give them the benefit of the doubt. But when someone squeezes my hand too hard, or squeezes it in the wrong direction (squeezing my knuckles together instead of squeezing the palm of my hand from top to bottom), that hurts! I wonder what the best way is to let someone know that they're hurting my hand. Just saying, "Ouch!" doesn't seem to get the message across. The person squeezing my hand just keeps on smiling and doesn't seem to notice that they're hurting me. What do you do when someone hurts your hand by squeezing it too hard?