Make Something Idiot-Proof, And The Universe Will Coin A Better Idiot

I work at a car wash at a gas station. We have some of those vacuums that you put quarters in. A customer comes up to me and complains.

Customer: “The vacuum isn’t working! I put a dollar in, and it won’t start.”

I go to check out the problem.

Me: “Oh, it looks like someone has blocked the coin slot with something.”

Customer: “You mean the money slot? That was me! It won’t take my money!”

She had tried putting a dollar bill in the coin slot; she had folded it up a bunch of times to try and get it in.