I did that on the dance floor of a small concert in NYC once. Everyone was jammed in tight in the first 5 'rows', but there was still room to dance a little. There was no way for me to exit the crowded dance floor in time, so I just let it rip. And of course nobody could hear it over the music. When it started to spread like over the crowd like napalm, I just looked around puzzled and annoyed just like everyone else was doing. Luckily after about 5 minutes it dissipated. Not my proudest moment, but I really had no choice. :)

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edit: This could be a TIFU, but it was 15 years ago. ;)