used to tell someone that you do not believe what they have just said

"Really, I'm very happy." "You could have fooled me." “真的，我很快乐。”“说得像真的一样。”

"What made you think I was cross? I wasn't cross at all." "Well, you could have fooled me."

"Anyway, it didn't bother me." "Hmm... you could have fooled me."

She insisted that she was fine with him seeing other women and I felt like saying, well, you could have fooled me.

"I didn't have a problem with Sam at all - I quite liked him." "Really? You could have fooled me."

See also: fool verb