I'm thinking of flipping out on a friend that went through my wallet
Why are you mad about your friend touching your wallet?
I didn't tell them they could touch my stuff
I understand why you would be upset. People should not touch someone's private things without permission but flipping out would only cause a fight. Instead, tell them never to do it again.
My friend is a twit and things will probably escalate.
You should try to talk to them in a calm manner. I know that they should not be touching your things, but it is still a little much to flip out on them for just touching your things.