Justin Bieber -- Sing Us a Song, Piano Man

Justin Bieber was slinging tequila and charming ladies with his piano playing and singing.

Monday night Bieber rolled into The Nice Guy in L.A. and was the nicest guy as he perched at the piano to sing two of his own songs and covered One Republic's "Apologize."

If that wasn't enough love to spread to the unsuspecting patrons, Biebs looked at a table of girls and dedicated a song to the birthday girl then bought all of her friends tequila shots.

We're told he made the rounds, asking people how they were doing as if he was the maitre d'.

Free impromptu concerts seem to be his thing lately.