I saw a really amazing one the other day.
I stopped by a local pet store. On the way in there was a huge standing sign nearly blocking the door. I thought "how rude!" and then realized the sign warned customers that their debit/credit network was down and all purchases would be CASH ONLY. I calculated and could still buy what I wanted, so I continued in.
As I was lined up by the till, I noticed another HUGE sign taped by the pinpad saying it was CASH ONLY. The person ahead of me was totally surprised by this but luckily had enough money to pay. She's not the special snowflake.
SS came storming in the doors and up to my cashier and said "Your store is the only one in town that carries my pet food, and I have three big dogs waiting in the truck and I'm double parked, you have to accept my Mastercard!"
The parking lot was EMPTY. I had rockstar parking and there were few cars around me. NO REASON for her to park right in front of the store doors. I could see her truck there.
The cashier said she was sorry, but they could only take cash. SS says "I WANT TO SEE A MANAGER!" Cashier calmly explains that the manager can't help, it's the computers that are down.
Then another customer defuses the situation by saying "Just go to the grocery store across the street, they have an ATM." The woman sputters a bit and leaves.
I have to admit that once the SS got started I was eagerly anticipating posting here and was kind of disappointed when the situation petered out.