NASHVILLE, Tenn. – The rapper Macklemore thinks there’s a simple reason the hit “Thrift Shop” appears to be going viral: It dares to be different.

“There’s a certain sound that has kind of flooded the mainstream airwaves as far as hip-hop music,” he said a few hours after taping a performance on “Late Show with David Letterman” last month with producing partner Ryan Lewis. “The beat doesn’t sound anything like that, the lyrics are kind of completely polar opposite from what you hear from most commercial rap records and it’s got a hook that’s very catchy. So I think that you combine those three things and it equates to an original sounding song that’s refreshing to the audience that hears it.”

Listeners have responded with rare enthusiasm to the song about “poppin’ tags” to develop your own unique sense of swag. “Thrift Shop” dropped last week to No. 2 on the Billboard Hot 100 radio airplay chart after several weeks at the top, is No. 1 on the iTunes songs chart and has been the No. 1 song on Spotify for several consecutive weeks. Only one other song, Bruno Mars’ “Locked Out of Heaven,” has reached the top of those lists simultaneously.

The Seattle-based duo has sold well over 2 million copies so far and sales continue to grow week to week. Macklemore, whose real name is Ben Haggerty, said he and Lewis thought the song might appeal to a “niche demographic” and didn’t envision it becoming a single. The song’s sense of humor is key, but Haggerty says there’s also a deeper message about individuality and modern culture’s obsession with expensive fashion.

“The more expensive the better is kind of the American way and if you spent $600 for a sweatshirt, then that makes it better,” Haggerty said. “And I don’t necessarily think that’s the case. If it’s a $600 sweatshirt that’s fresh, that’s fantastic if it looks great. But to me to just pay a ridiculous amount of money for something just because of the logo isn’t creative and it’s just unfortunate that people equate spending money to style.”