1. I told my parents that I had gotten passing grades in all my classes, but they didn’t believe me. They called my bluff and asked to see my report card.
2. The bank robber threatened to shoot the bank guard, but the guard called the robber’s bluff by walking up to him and taking away his gun.

This idiom is based on the literal meaning of this phrase as used in card games such as poker. A player who is bluffing may pretend to have a winning hand when in fact he or she does not. To call one’s bluff in poker is to challenge one to show his or her cards.