It would be nice if there were no more injuries associated with this problem. And, I agree with Trillian: now that he knows this will set you off, you can expect him to mess with your chameleon every chance he gets. Locking the room would be the best option, if that's impossible, putting a lock on the cage would be appropriate.
Your parents should be informed and you should tell them that if your chameleon needs medical care, your brother should pay for that. They need to understand that this was a "prank" with the potential to cause extreme damage and cost a great deal.
I agree! Lock your brother in a room! And yes, it would be a bonus to lock him in a cage!
Seriously, I hope your cham is alright, and thank goodness you got there when you did!