Please, don't throw poor guy's camera overboard. Then, 1) you are littering and 2) he'll just get a new one 3) you'll be the bad guy in the story.
Oh, I don't think I need to say this, but please don't start an underwater knife fight with him either
If you want to actually change his behavior you'll have to have a pretty uncomfortable conversation. The hard but crucial part is avoiding triggering the fight or flight response in him. So if you start with "WTF, dude you're breaking all the coral" or "your buoyancy sucks, you need to improve it" you've lost already.
You need to determine the root case. Does he a) not know he's doing it because he's a new diver and lacks awareness or b) knows but doesn't care.
If a) you need to make him aware without making him feel ashamed. Mention that you've done it too (like you did in the OP). Maybe give him buoyancy tips.
If b) You can tell him how long it takes for corals to grow, how if he keeps breaking them, there won't be any cool dive sites soon. Suggest ways for him to take pictures in a safer way. I'm not a photographer so I don't know how people do it in current. One total guess is using a reef hook. Would that be a good idea?
Don't make him feel like the bad guy, empathize with him, figure out why he's doing it and find a way to get him to get what he wants without breaking all the coral for the rest of us.
Good luck! If you can make him actually change his behavior the impact is a lot bigger than just him. Think of all other people in the future who'll see him and think what he's doing is ok.
