You’ve got another think coming

you've got another think coming

Your expectations are wrong and unreasonable; you better think again. Almost always preceded by "If you think (something)." The phrase is commonly altered as "you've got another thing coming." If you think you can walk in here and just demand a raise, you've got another think coming. If he thinks he can hit it big without paying his dues, he's got another think coming.
See also: another, coming, think
Farlex Dictionary of Idioms.

You’ve got another think coming

sent. You have made an error. Think again. (Especially with if. The word think is original, although some speakers change this to thing.) If you think I’m going to let you get away with that, you’ve got another think coming.
See also: another, coming, think
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions
See also:
  • you've got another think coming
  • have another thing coming
  • you've got another thing coming
  • have another guess coming
  • have another guess coming, to
  • quit (some place)
  • quit a place
  • go against the flow
  • What are you on?
  • never in a month of Sundays