This was almost 10 years ago or so, but still sticks in my memory, especially now that Glee has risen to such popularity.
My friend and I were at a festival on Toronto island several years back, one of those ones that Sloan put on. To put in perspective how long ago it was, Death From Above (1979, now) was the opener and Arcade Fire played second. The thing about Toronto Island, if you've never been, is that it's an island of course and as such, you have to take a ferry out there. On a normal day this isn't much of a problem, as the traffic is steady, but not jammed. On this day (and any other event day), the ferry dock is a bottleneck at both ends throughout the day. Only one ferry can load at a time, so each shore was busy for a portion of the day.
We got over relatively early, which meant not a lot of waiting. When the night was closing up and Sloan went on, we thought we'd be the savvy concert-goers and take off after 4-5 songs. It became immediately clear that we weren't the only ones who had thought of that. The wide path leading to the port was jammed ten-wide and several deep, chugging along very slowly. We got about 40 people deep when the gate closed and the ferry took off, accompanied by a collective groan from all of us. Just then, two guys got up on the railing and said, 'Hey, it's no problem - we'll make waiting fun!' Before anyone had a chance to figure out what was going on, they broke into a full-volume version of Bohemian Rhapsody. Normally, this would be silly and cringe-worthy, but they were actually really good. They picked the perfect song to get everyone involved and that they did. Very quickly it became roughly 200 of us singing along, harmonizing and pumping our hands up. Then, just like Glee, it ended with very little fanfare. There was a bit of clapping and they announced that they were part of a performing group that would be playing the following week at some place, then everyone returned to normal. The ferry arrived and we all returned to our lives as if it were a normal thing to spontaneously burst into song.