Aussie Model Rips Kim Kardashian's Ass

5/6/2010 5:15 AM PDT

Australian supermodel Sophie Turner is trying desperately to take the booty crown from Kim Kardashian -- and Monday night, Sophie even engaged in some serious backside trash talk.

As she flexed her gifted glutes outside a nightclub in Hollywood, Sophie took a shot at her competition saying, "At least mine's real."

For the record -- Kim has always claimed that her butt is 100% authentic.

Butt we gotta ask ...