A few friends and I are going to a concert in a few months. I bought the tickets for everyone, so I could make sure we would all be sitting together. Everyone agreed to pay me back. I didn't give a deadline, but I figured it would be sometime soon.

I see these friends regularly, and only one has paid me back so far. I hate asking for money, and I don't want to ask them for it in a group setting, which is how it is whenever we hang out. However, it's been 10 days since I bought the tickets, and the ones that haven't paid me back, haven't even mentioned it to me. I think they may have forgotten. Should I remind them, or wait a little bit? How often can you remind someone without being annoying?