go mental

1. To become extremely angry or upset. My parents are going to go mental if they find out we had a party here! Don't go mental, but I think I broke your computer. Mom and Dad will definitely go mental when they see you're failing three classes!

2. To become or feel crazy. I'm going mental being stuck in this cabin all week with my parents! Have I gone mental? When did rents in this part of town become so expensive? I'll end up going mental if I have to work in this cubicle for one more day!

3. To act in a crazy, foolish, or reckless way. Too many kids start going mental when they go to college and have total freedom for the first time in their lives. Have you seen the way he's spent money lately? It's like he's gone mental! Danny's a teenager, he's going to act out. Just make sure he doesn't go totally mental.

go ˈmental

(British English, slang) become very angry: My dad’ll go mental when he sees what we’ve done!

go mental

in. go crazy; to act stupid. Another day in that history class and I know I will go mental.