So I started singing "El Scorcho" by Weezer. I got one line in and was feeling pretty pleased with myself to be part of the "in" crowd that knew the signal. Then Jeff's date caught my eye, smiled, and joined in with me for the second line. I smiled, too; this was clearly someone in the know. I continued walking down the street, and as I continued singing, more and more people starting picking it up and singing along with me. Before I knew it, half the crowd in the park along an entire city block was raised up in happy unison, singing Weezer. What a good time!
So, yeah, if you're like me, and you not only marveled at those scenes in musicals where the whole town joins in with the song, but also wondered what that might be like in real life: it is as awesome as you hoped.