Shia LaBeouf Arrested After Being Thrown Out of Studio 54

Shia LaBeouf was ARRESTED after acting crazy in a New York City club, then threatening cops and club security.

Shia was at a showing of "Cabaret" at the legendary Studio 54 Thursday night ... when he was smoking inside -- which is against the law -- and "alarming people" by his conduct by being extremely loud and obscene.

Witnesses say Shia appeared extremely drunk, reportedly played grab ass with some of the actors on stage and then flew into a rage, spitting on people.

As for the threats to law enforcement ... Shia reportedly told police, "I'll f*** you up."

Police came and arrested the actor and took him to the cop shop. Shia was charged with criminal trespass and disorderly conduct.

Shia pled not guilty Friday morning and left the courthouse a free man.