"I'm going to tell Billy what you said about him." "Don't you dare! "
don't you dare
An emphatic way to tell someone not to do something. Don't you dare say something vulgar like that to your mother!Don't you dare touch that autographed baseball—it's worth a lot of money!
don’t you ˈdare (do something)!
(spoken) used to tell somebody strongly not to do something: ‘I’ll tell her about it.’ ‘Don’t you dare!’Don’t you dare say anything to anybody.