The desk manager at my hotel in Rhiyad Saudi Arabia. Leaving to go shopping I give him a crisp 100 US. He gives me the equivalent in riyals. Off I go. Upon returning I hear a loud Arab voice saying something in gibberish to me but realized he's looking directly at me with a 100 bill in his hand. He said it's fake. He rubs it on a piece of paper. Ink comes off. Fake. I give him another hundred and take "The fake" back. (Those 100's came directly from a bank in the US) Anyway, I assumed I was scammed as he gave me the fake and kept the real, obviously I spent the "fake" somewhere else without being unknowingly caught or possibly ink on US bills do rub off? I never tried, but I doubt it.