Oh, I've got a clear pick for this one.

This was in high school. I was in Boston with one of my best long distance friends (I met at a camp) because we had both been chosen to premier the organ works of a composer at a music convention. My friend came down for two days and we hung out a lot with all the other high school kids at the convention. On the last day she was there, my organ teacher told me there was some concert he really wanted me to go to, so I stopped hanging out with my friend to go to the concert. It was the most boring thing in the world, the organist played all Bach and had the most boring performance and didn'f say anything and no one was allowed to clap, and the organ was no good. I was bored out of my mind the entire time anything this presented about 2 hours I could have spent with my friend. Then after the concert I called her so that we could eat dinner before leaving and she said she already left because the events were over and no one was there. That was the last time I saw her four years ago.