You just can't make this up.

So, I have this regular customer; he comes in at least once a week, sometimes more often. With this customer, I can guarentee that at some point during his time in the store, he will want to break a $20. And from past experience, he seems to greatly prefer getting two $10 bills.

Him: Can I get change for a $20?
Me: Sure. I know I have two $10s. (If I just say sure, he asks if I have $10s. I thought I would anticipate him.)
Him: You don't have any $5s?
Me: Yes, I do.
Him: Okay, two $10s please.

*head asplode*