Have another think coming
Meaning: Be deluded and have plans that won't happen
Originated in: 🇺🇸 United States of America
Earliest attestation: The Syracuse Standard, (May 1898)
Saying someone has another think coming is a somewhat clever way of saying he is wrong about his expectations. He thinks one thing—but in time his expectations will be dashed, and he will have to think about it again. It is typically used as a warning to someone who is overly confident or arrogant, often with the perceived delusion restated in the rebuke: “You think you’re going to win? You have another think coming!”
Given the phrase’s bit of humor, it can be a light way of telling someone his plans are not going to work out. However, it typically is quite a confrontational phrase, and it is often used in a more serious context.
In the United States, the variation “have another thing coming” is more common. The two phrases mean exactly the same thing however.