Is it normal to get mad at this?

They should be more respectful of what you're asking of them, due to it being your property. You have every right to tell him not to mess with your stuff, especially if there is a chance he may break it.
She needs to understand this and explain this to her brother, it's very disrespectful and inconsiderate; besides would they be all happy go lucky if you went over to their house and started messing with their property without permission and possibly breaking something?

Do the same with you gf stuff, so she'll get mad at her bro when he do that. Later on do it to his stuff. Problem solved :)

She's probably upset because she doesn't know how to tell her brother and feels bad about it. :/ do y'all all live together?

I feel the same with little kids. There parents/siblings always think that there mature enough to handle my more expensive items but i feel like there going to break it. I love little kids but it really annoys me.

I don't have an answer for you, except that I sympathise. I hope he grows out of it.

I too would be annoyed. But there doesn't seem to be an easy way out of the situation.

Thats annoying. Your gf sounds immature. You're right for being annoyed. Talk to her about it and if she's still stank about it smack that bitch and leave.

id be mad too, who wouldnt, youll have to tell him but pick one thing at a time. start with the phone. future ex wives :)

He sounds like a shit.

Oooh! Everytime he fucks around with one of your possessions whilst both you and your girlfriend are in attendance fuckin, punch your girlfriend in the face. After a while youll Pavlov mind fuck and condition her to not let her little bro fuck with your shit. Every time he goes to fuck with your shit and she sees it, she'll think, Oh No! Not another punch in the face and stop him. Works for my future ex wives. And day saved, Im going on break.