Definition
This idiom is used to describe someone who behaves in a peculiar or eccentric manner, suggesting they might be slightly mentally unstable.
腦袋有問題（形容行為怪異）
He started singing loudly in front of everyone; I think he has a screw loose.
他在大家面前大聲唱歌；我覺得他有點不正常。
She went to work in her pajamas yesterday, I'm starting to think she has a screw loose.
她昨天穿著睡衣去上班，我開始覺得她有點不正常。
How could you put your keys in the refrigerator? Do you have a screw loose or something?
你怎麼會把鑰匙放在冰箱裡？你是不是有點不正常？