Definition
To behave in an extremely foolish or absurd manner.
脑袋有问题
He tried to open the can with a fork, he must be off his nut.
他试图用叉子打开罐头，他一定是疯了。
You put your phone in the washing machine, you must be off your nut.
你把电话放进洗衣机里，你一定是疯了。
She actually believes aliens abducted her cat; she's completely off her nut.
她真的相信外星人绑架了她的猫；她完全疯了。