Not so grateful bank teller

I cashed a check today, and after she counted the money 6 times, yes, I said SIX TIMES, she handed it to me and I went on my way. Walking to the car, however, I felt this ping of something telling me to count it again. I was taking my old intern, who had come back to visit, to lunch. So I got in my car and drove off. The entire way knowing that I had to count the money she gave me. We walked in, ordered, and I opened my wallet. Sure enough, she had given me $20.00 too much. And all I kept thinking about was that scene in The Family Man where Don Cheadle is the angel...and the clerk at the convenient store. Remember that? This girl comes up to buy a pop and hands him a dollar bill. He takes it, says, "Change from ten," and proceeds to give her $9.00 back. She looks at him, astonished that he thought she gave him a ten. He asks her one last time if there was anything wrong, she says no, takes the money, and walks out. He watches her leave and says, "Man...character. And for what? A lousy nine bucks?" I kept thinking that over and over again...that I knew I needed to return it. Her drawer would be off by $20.00. There was no way I could keep it. But there was that moment. That little moment when you think, Well, it was her fault. She messed up. She counted it six times. It's only twenty dollars. And you'd be right. It is only twenty dollars. Would you really jeopardize yourself for a lousy twenty bucks? You don't know what load that teller was carrying today. You don't know if she was having an awful day, if her boss just yelled at her for messing up, if her kid is sick, if her car broke down. Haven't we all had one of those days? So, after lunch, I drove back to the bank. Walked in, and quietly asked if she remembered me, and told her she gave me more money than I should have gotten. She took the money, gave me a half smile, and said, "Huh. Oh." I turned and walked out. Really?? Did that seriously just happen?! Where have everyones manners have gone!? A thank you would have been nice! Especially since that $20.00 could have gotten me a pair of shoes at Target.