woe betide (one)
Unpleasant things will happen to one. And woe betide anyone who tries to ruin my plans!
woe betide (someone)
1. Used to express the wish for someone to experience misfortune.
2. Used as a warning or allusion to negative consequences: "Even though my dad was no farmer, he was a crack shot and a very good hunter&.... woe betide the unwary moose that wandered down from Canada" (Howard Frank Mosher).