said when there will be trouble for someone, or someone will be punished, if they do a particular thing(某人)要倒霉(或遭殃)
This is the second time he's been sent home from school this month, so woe betide him if it happens again!这是他本月内第二次被从学校赶回了家,要是再发生一次这样的事,他就要倒霉了。