have another think coming

have another think coming

(One's) expectations are wrong and unreasonable; (one) better think again. Almost always preceded by "If (one) thinks (something)." The phrase is commonly altered as "have 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, have, think
Farlex Dictionary of Idioms.

have another think coming

 and have another guess coming
to have to rethink something because one was wrong the first time. (Think is a noun here.) She's quite wrong. She has another think coming if she wants to walk in here like that. You have another guess coming if you think you can treat me like that!
See also: another, coming, have, think
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.

have another think coming

If you say that someone who thinks a particular thing will happen has another think coming, you mean that they will discover that this is not correct. If he thought he was going to rule her, he had another think coming. If you think that I am driving all the way to Donegal with that noise going on in the background, you have another think coming. Note: This expression is usually used to show that you are angry at what the person wanted and will not accept it.
See also: another, coming, have, think
Collins COBUILD Idioms Dictionary, 3rd ed.

have (got) another think coming

used to express the speaker's disagreement with or unwillingness to do something suggested by someone else. informal
2000 Sunday Herald (Glasgow) The accelerating pretender has another think coming if it imagines that it has an easy shot at becoming world number one.
See also: another, coming, have, think
Farlex Partner Idioms Dictionary

have another think ˈcoming

(also have another thing ˈcoming) (informal) used to tell somebody that they are wrong about something and must change their plans or opinions: If she thinks that married life is going to be easy, she’s got another think coming.
See also: another, coming, have, think
Farlex Partner Idioms Dictionary
See also:
  • You’ve got another think coming
  • you've got another think coming
  • you've got another thing coming
  • have another thing coming
  • have another guess coming
  • have another guess coming, to
  • the dust settles
  • even better
  • dragged
  • devil take the hindmost