(When I ring out customers with small items or few things, I ask if they want a plastic bag in the interest of not wasting one on something small.)

Me: “And did you want a bag for your pen, sir?”

Customer: “No, thanks. I just want the receipt. Save the tree.”

Me: *looks questioningly* “Sir, the bag is plastic. It doesn’t come from trees.”

Customer: “Whatever. Something about dolphins and the Amazon…” *walks out*