I am with you mrsbrandt. I just keep imagining the post from sis's POV...
"I asked my sister two weeks ago if she'd babysit my kids. I always assure her that I will understand if she can't/doesn't want to babysit. Sis told me she'd be happy to babysit so hubby and I could go to a cooling class together. It is his/my Christmas present. Two weeks later, a few hours before we are supposed to head to class, I get a call from sis. It seems she has had tickets to a concert tonight. In fact, she has had the tickets for 2 months. It sems she and bf never checked the date on the tickets and thought it was next week. Sis asked if I could find someone else to babysit but said if i couldn't she would skip her concert.
I didn't know what to say. If I had enough warning I would have had no problem finding another babystitter. I started to stress about who, if anyone, would be available. I certainly didn't want to make sis miss her concert because that would also effectively ruin her bf's night as well. I finally decided to call mom and ask her to babysit the kids, though I was reluctant to ask mom because (insert personal reason here). By the time I explained to the kids that auntie wasn't coming over like we thought, the excitement of my night out had faded a little. Luckily, Mom could babysit, though I was still a little concerned because (insert explanation here).
The next morning I'm driving to work with sis (we carpool) and I was still a little grumpy becasue of all the last minute scrambling I went through the day before. I tried to avoid to much conversation with sis but she kept pushing me to talk. Finally I told her I was disappointed by her and just needed a little while to get past it. Sis offered to babysit this weekend for free and I did assure her that that made me feel better but I was still kind of hurt and upset that she put me into an uncomfortable/stressful situation just because she and bf didn't know what night their concert was."