Bieber is starting to pick up on the nasty celeb habit of tweeting outrageous pics.

It all started with a the infamous pic of him smoking what looked to be a marijuana joint - which sent his young fans into a frenzy and started the #CutForBieber trend in protest to his using drugs.

And now the star’s tweeted a pic mooning his fans as some sort of prank, I presume. 

Even though he was quick to delete the image from his Instragram, this will probably go down in the books as one of the most distasteful pranks the youngster has pulled.

#BriefsForBieber anyone?

Take a peek at the pic here.

Justin’s butt is: