I once had a cafeteria lady at school be this confused. She have me $10 back when she only owed me $0.50 and I paid using a $1 bill. Not sure what she was thinking but she assumed I was trying to get her to give me more money and called security on me. I didn't bother explaining it any further and kept the $10. I made money and got my cookie for free. I considered it an inconvenience free.