Joking Is Not In His Blood

(I work as both a box office and concessions employee at a locally-owned movie theater, where our policy is to have every customer sign their receipt for us. This happens as I watch one of my coworkers finish up a transaction:)

Coworker: “Okay, sir, here’s your card back, and I’m just going to need you to sign right here for me!” *holds out a pen for the customer to take*

Customer: “What, am I supposed to sign with a pen?”

(I can tell right away that the customer is not joking. I let out a tired sigh, and then step forward.)

Me: “No, sir, with your blood.”