Billy, What Have You Done

BUT THERE IS NO BRAIN

It isn't though because it is just stupid.

Actually, it's not a valid comeback, because you're just saying two words but one is just not the correct way, valid comebacks have effort put into them while "No u" is just lazy as hell, you just say "No u" because you can't think of a valid comeback, and that's all I have to say-

It is a valid comeback, just annoying as f sometimes.