Justin Bieber I'm Just So Damn Tired

11/11/2015 6:26 AM PST

Justin Bieber -- I'm Just So Damn Tired

Justin Bieber offered up a clue on why he went off the rails in Europe ... he's just really tired.

Justin showed up with French Montana at 1 OAK Tuesday to celebrate French's birthday. People inside the party tell us Justin was chill ... his drink of choice was Hennessy straight.

Nothing like a relaxing night out on the Sunset Strip.