It's a very tricky thing to correct someone on the social dance floor and in my opinion really should never be done, even by teachers. It's not your place. Corrections are for the classroom or practica. (Warnings about floorcraft are sometimes given by the organizer of the milonga - I've heard this done and no one is offended.) If you really think someone ought to say something to him then go ahead and speak your mind, but chances are you will just offend him and he won't listen anyways. (People usually brush off corrections that are given to them on the dancefloor by thier peers.) But if you are getting so bruised by dancing with him then why would you care if he stops asking you? If he really is a hazard, then you should probably turn him down anyhow -- maybe that will give him the message that he needs to slow down.

But, if you choose not to say anything, there are a couple of things you can do to help avoid collisions.

First, keep your eyes open and if you see that he is about to step into someone, try to stop him...squeeze his hand, press his shoulder, inhale sharply, squeal...these all work!

Second, and very importantly, guys are not the only one who need to be careful on crowded dance floors. If there are lots of people around, be conscious and keep your feet on the ground. Just because your partner leads a boleo doesn't mean you have to kick your leg up behind you. Boleos come from a snap in the hips, not a lift in the leg, and you can do them with your feet together. Sometimes the snap is even more powerful when you do them this way, as none of the energy is diffused into the legs.