Verb
woe betide
(transitive, idiomatic, humorous or literary) Used to warn someone that trouble will occur if that person does something: bad things will happen to.
Woe betide you if you try that with my sister again!
I cherish my privacy, and woe betide anyone who tries to interfere with that. Jeff Beck
Woe betide the leaders now perched on their dizzy pinnacles of triumph if they cast away at the conference table what the soldiers had won on a hundred bloodsoaked battlefields. Winston Churchill
A painter may know what he does not want. But woe betide him if he wants to know what he does want! A painter is lost if he finds himself. The fact that he has succeeded in not finding himself is regarded by Max Ernst as his only 'achievement. Max Ernst