that'll teach someone idiom
这下（某人）该知道（做某事的）后果了，这下（某人）该知道（不应做某事了）
used to say that a person should avoid doing something bad in the future thanks to the experience of the effects of their actions
So Roger spent the night in a freezing garage, did he? That'll teach him to (= show him that he should not) go out without his house keys! 这么说罗杰在冷冰冰的车库里过了一夜是吗？这下他该知道出去不带房门钥匙的后果了吧！