Khloe and Kanye aren't stupid -- they're not gonna wear their designer best in the rain!

The two KUWTK cast members dressed down for a rainy day of taping at their Calabasas studio. Kanye wore a khaki waterproof windbreaker to match his blonde-ish/khaki-ish hair color , black sweatpants, and black Yeezys.

And though Khloe wore rubber slides, she did accessorize with a baby blue baby Birkin! And her biggest, baddest accessory of all was her new Rolls Royce SUV! You've GOT to see how she maneuvers the $250K ride out of the studio parking lot -- she almost CRASHES that bad boy!!! Watch the video!!!