call somebody's bluff

call (one's) bluff

1. To challenge someone to act on their threat or prove that their claim or boast is true, when one believes they are making a false claim or idle threat (i.e. bluffing). He insisted that he could run faster than me, but when I called his bluff, he suddenly said he had to go home.
2. To disprove a bluff. Whereas the first usage simply indicates a challenge, this usage indicates that the challenge resulted in the disproval. I don't know why he keeps making these outrageous claims. I've been calling his bluff for years and making him look like a fool.
See also: bluff, call

call somebody’s ˈbluff

give somebody the chance to do what they are threatening to do, because you believe they will not or cannot do it: Next time she offers her resignation, they’ll call her bluff and accept it.
If you call somebody’s bluff in the game of poker, you force them to show their cards.
See also: bluff, call