I'm so mad at my dormmate I'm going to break his expensive camera.
That sounds terrible! Why would you break his camera on purpose?
He borrowed some of my things and broke all of them!
I'm sure you're upset at your dormmate for what he did to your things but breaking something of his as an act of retribution is wrong. Talk to him and tell him how upset you are for his actions. Make him understand that he needs to apologize to you for damaging your things.
He's selfish and careless, he won't change.
Talk to him and see if you can get him to understand why you're so upset. If that doesn't work, don't lend him anything again so you won't have to worry about it being damaged.