This is no joke. Justin Bieber is teasing that he's going to be playing Robin in the upcoming Batman Vs. Superman movie.
Bieber just posted an image to instagram of himself with a copy of the Batman Vs. Superman script with a Bieber watermark on it. Bieber also posted the text, "#robin ??".
Now, it could very well be that Justin Bieber is just playing a little joke with the Robin hint, but the photo still raises the question of why he has a script. If he was just doing a song on the soundtrack or something, then it probably wouldn't require for Warner Bros. to provide him with an entire script.
Could he be up for a role in Batman Vs. Superman? Or could it just be a fake script? If the script is real, then it confirms that the title is Batman Vs. Superman. One interesting thing about the script is that it says based on Batman: The Dark Knight Falls, and in that particular comic Robin was a girl. We're thinking that it's got to be a fake script, but who knows at this point.