Kim Kardashian -- Nothing Says 'Thank You' ... Like My Ass in a Thong

Major props to Kim Kardashian's Instagram minions -- because without them ... you wouldn't be staring at her bare ass cheeks right now.

Kim uploaded a shot of herself sporting a thong -- ass-side up, of course -- to her Instagram account to celebrate reaching 27 million followers.

For what it's worth ... it appears to be a throwback pic, since Kim was in London Wednesday night (for the Brit Awards) -- we're doubting she packed swimwear.

There. Don't say she never did anything for you.