You'll hear it piped through the speakers in any trendy chain coffee shop or other place hipsters have historically gathered. You'll know it by the hesitant guitar notes and presence of "new cool" instruments like the ukulele. The singer usually mutters his verses with extreme trepidation. The singers' vocal styles range between high-pitched, like a candidate for a boy's choir, or brassy, like a reject from Muppets voice acting tryouts. The themes behind the songs are usually so safe to the point of being insipid -- travel, relationships, sometimes something so trivial as "it's raining."
Hipster music is unobtrusive; it knows it's not the reason why people go to coffee shops. It never comes to the fore because it's not mainstream, it's not corporate ("You just don't get it, man!"). It hasn't sold out, or at least it claims it hasn't. Its image depends on its audience not knowing it has, in fact, sold out to The Man.
Oftentimes, the volume is turned low so the music provides a barely-audible back beat to the chatter in the café, although sometimes it's annoyingly loud. On that note, when it's turned up too loud, it's really annoying because the genre seems to be about music that doesn't want to be heard. The vocalists mumble. A mumble that sounds like a roar is paradoxical, it's something you don't come across every day and when you do, it seizes your attention and doesn't let go. Like a train wreck. It's an awful thing to see and you don't watch it because you want to, you watch because it's something you don't get to see every day -- whether you want to or not.
All this begs several questions: who listens to this? Does anyone? Were you to go to the music store, would you find a section devoted to coffee shop music? Would you feel embarrassed at the look you'd get from the music store clerk on asking him where that section was?
On that last note, if you'd feel embarrassed at all, it's probably because you know what you're doing is wrong. Take off your scarf, it's a hundred degrees out. And take off your sunglasses too, you're indoors. Spit out that cigarette, it's not even lit.
Friends don't let friends listen to Hipster Muzak.