Believe it or not that $2 bill happened to me not long ago. I was at Walmart and had a worn out two dollar bill in my pocket... wasn't worth anything more than face value. I gave it to the teenaged cashier and she looked at me like I had two heads. Then she grinned and asked "Is this for real?" I told her "yes ma'am that real legal tender" And she looked around like she was looking for a hidden camera. Again she grinned and said "I gotta call my manager". Before she could do it though one of the older cashiers walked up and and just grinned and winked at me. She told the younger gal, "honey go ahead a ring this gentleman up that money is real, it's just before your time." She then looked at me and rolled her eyes and shook her head. It was funny and we all had a giggle at it.
Be a radical... use common sense.