Khloe Kardashian -- On Kim's Ass For Title of Hottest Kardashian Ass

Watch your back, Kim ... Khloe is coming for you.

Khloe Kardashian continued her all out assault on her sister's claim to the most colossal culo in Calabasas ... as she was spotted leaving a private gym Tuesday afternoon.

The spandex-clad profile is oddly similar to the one Kim showed off just a few months back.

The question is ...