It's not only at First Avenue's Main Room, The Cabooze is definitely another place that comes to mind. The Dakota Jazz Club and even the last show I saw at The Artists Quarter, but recently, First Avenue's Mainroom and the 7th Street Entry seem to attract the most guilty (let's be honest, mindless hipsters who are often just there to "be there" and not for the music itself).
But this t-shirt pretty much says what I'd love to remind those tactless people.
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Also see the line in Devin Townsend's "Earth Day"
"Listen to me! Just shut the fuck up!"