guess again
A rhetorical imperative indicating that the person being spoken to is mistaken about, and thus should reconsider, something. You'd better guess again if you think I'm going to lend you any more money. If you think you can walk in here and just demand a raise, guess again, buddy. I know you said he would never show up, but guess again, because here he comes.
Farlex Dictionary of Idioms. © 2024 Farlex, Inc, all rights reserved.