We still don't quite know what was going on here. Justin Bieber tweeted this photo, captioned "2 much fun." In the shot, Selena Gomez and The Biebs are laughing hysterically -- but, teases that they are, they won't reveal why!

With these two, it really could be anything. Based on his other tweets, his television appearances and his interviews, it's pretty clear that Bieber has a silly sense of humor. Gomez demonstrated her comic timing beautifully on 'Wizards of Waverly Place' for a pretty long time.

Maybe she just got punked by her 'Boyfriend' singing boyfriend? After all, he did it to Taylor Swift, Rob Dyrdek and his own fans -- we don't think Sel would be immune!