Kourtney Kardashian — Suns Out Buns Out (PHOTO)

Kourtney Kardashian was really feelin’ it Sunday … in a super skimpy bikini.
Interesting … Kourtney posted the pic on social media a day after Justin Bieber posted a throwback of him with ex-GF Selena Gomez.
So at the risk of overthinking it, she’s telling Biebs … butt out.