To give your signature or consent on a form where you have not read all of the fine print. Many of us fall susceptible to this when checking off the 'I Agree' box in user-agreements for websites or software.
Person 1: Oh, I already signed the contract.
Person 2: ...that was fast. Did you remember to read all the fine print?
Person 1: No. Why?
Person 2: How could you be so damn signorant?