Photo of the day: Justin Bieber almost shows off his D

God knows we woulnt have been moved if he lifted that guitar a bit.
Sources say JB had been staying at his granny’s house during the holiday … and slept in a little too late on Thanksgiving morning.

Bieber finally woke up after hearing family and friends stirring around the house — so he thought he’d prank ‘em … by grabbing his guitar and playing a naked set a la Jenny from “Forrest Gump” (‘memba that?).
We’re told birthday-suited Bieber went right up to his grandma and started belting out some impromptu lyrics … like, “I Loooove you grandmaaaa … how are youuuu … helloooo grandma.”
We’re told G thought it was pretty funny — and everyone in the home was cracking up — but granny begged the pop star to get back in his room to put some damn clothes on, stat.
Thanksgiving — they go balls out.