Robert Pattinson -- SHUT OUT of Justin Bieber and Katy Perry's Party Bus

Twilight, shmilight -- Robert Pattinson was fully dissed last night when he couldn't catch a ride with Katy Perry, Justin Bieber and Selena Gomez.

The unbelievable scene went down last night at Chateau Marmont ... where Biebs, Selena, Robert and Katy were all hanging after Katy's movie premiere.

When the posse made its exit, Bieber, Katy and Selena all piled into a limousine bus -- surrounded by heavy security.

Unfortunately for Pattinson -- who was hangin' with "Raising Hope" star Shannon Woodward -- the bodyguards left them out in the cold.

Unreal.