Yes. I did that a few months ago, actually. I was at in the washroom of a club and saw the $20, and looked around to see that no one saw it and no one was really around it. I waited for a group of girls standing nearest to it to leave and then picked it up. I figured that the whoever dropped it had left the washroom and may or may not come back looking for it, and if I hadn’t picked it up, someone else (most likely not the owner would have) and they probably would have bought drinks with it. I wasn’t drinking that night, took it home and it went in the bank. That’s how I rationalize it, but I had initially wanted to donate it to a charity, and I didn’t get around to it. This post, having reminded me, makes me feel like I should.