A few years ago I remember a story going around about someone trying to use a $2 bill at a Taco Hell. Snopes doesn't have any indication as to if it is true or false, but it seems that there are some people out there who still aren't familiar with $2 bills.
A Baltimore man tried to pay for a Best Buy car stereo installation with $2 bills—and was arrested. Apparently the man was already upset with the Best Buy's service, so thought he'd stage a minor protest by using the uncommon currency:"I'm just here to pay the bill," Bolesta says he told a cashier. "She looked at the $2 bills and told me, 'I don't have to take these if I don't want to.' I said, 'If you don't, I'm leaving. I've tried to pay my bill twice. You don't want these bills, you can sue me.' So she took the money. Like she's doing me a favor."(Thanks, C0bra!) Gizmodo]
He remembers the cashier marking each bill with a pen. Then other store personnel began to gather, a few of them asking, "Are these real?"