Justin Bieber -- He Picked Wrong Town to Screw Up in ... Says Miami Beach Mayor

Justin Bieber's gonna face the full wrath of the law after his arrest for DUI and drag racing ... so says the top dog in Miami Beach, Mayor Philip Levine.

Shortly after Justin's bust, Hizzoner was in Washington D.C. for a conference ... and told us folks in his city won't stand for Bieber or anyone else recklessly speeding while drinking and driving.

And if Bieber thinks he's gonna get special treatment while he's in custody -- the Mayor's got a strong opinion about that ... though he left a little wiggle room.