Irina Shayk -- Nothin' But My Red-Hot Bikini N' Boots!

"These boots were made for walkin' ... and fashion model Irina Shayk is about to "walk all over you!"

Check it out -- Irina, 39, effortlessly blasted a handful of sexy shots to social media, wearing nothing but a red-hot bikini and black boots!

Leanin' back in her chair, here's a shot of Shayk shakin' things up by doing absolutely .... nothing!!