If you’re wondering why the phrase “nip slip” is suddenly trending worldwide on Twitter and other sites, there’s a simple (but totally insane) explanation.

Harry Styles, a member of the uber-popular boy band One Direction, tweeted a photo of fellow band member Niall Horan playing guitar with his nipple out and the phrase “nip slip” as a caption. And now it seems that photo is all anyone's talking about on Twitter.

The English-Irish boy band has developed a strong and oftentimes rabid fandom since the release of their 2011 debut album, “Up All Night.” Their debut single, “What Makes You Beautiful,” quickly gained fame through social media, leading to the rise of the fandom known as Directioners.

Because the members of One Direction have such a strong social media precence on sites like Twitter, Facebook and YouTube, millions of their fans flock to these sites, particularly Twitter, to express their fandom and obsession with the boy band.

And Thursday’s “nip slip” tweet proved just how powerful fans of the band can be. Less than 30 minutes after Styles tweeted the photo of Horan, the phrase “nip slip” quickly began trending worldwide on Twitter, MSN Now and other social media trackers.

One hour after Styles’ “nip slip” hit the Internet, the tweet had already received 55,524 retweets, 58,755 favorites and countless replies. Because the One Direction fan base is so particularly devoted to the band, the tweet became extremely popular very quickly.

And One Direction fans have a lot to say about the photo.

“the picture of harry sleeping like an angel??? oMG AND NIALL WiTH THE NIP SLIP LORD JESUS HELP mE,” one fan wrote.

“Lmfao, Nip Slip trending worldwide:') but tbf, Niall has a hot nipple,” another commented on the exposed nipple.

“Niall's nip slip is simply is the sexiest thing I have ever seen in ky whole entire life,” another fan wrote, though she didn't bother to check her spelling before posting.

Nip Slip. oops theRE WENT MY OVARIES ALL THE WAY TO MADAGASCAR,” read one particularly confusing tweet.

It should also be noted that many of the fans tweeting about the post had almost exclusively One Direction-related content on their Twitter feeds. Many have One Direction background images.

There’s a serious lesson in all of this, though. Never underestimate the power of an exposed nipple.