You could've fooled me

You could've fooled me.

  (informal)
something that you say when you do not believe what someone says about something that you saw or experienced yourself 'No, I wasn't angry, I was just a little surprised.' 'Really? You could've fooled me.'
See also: fool
References in periodicals archive ?
But with all those restaurant lunches and pub suppers, you could've fooled me.
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