RIHANNA IN HER UNDIES? YOU THINK YOU'VE SEEN IT ALL UNTIL YOU SEE HER THONG' OUT HERE!

Rihanna thought of celebrating her newly acquired boots and she instagrammed the pic ... accompanied with the message: 

"Gotcha bitch tip toeing on my marble flo'!!! Sick ass custom Prada boots! Miuccia you RULE!!! Thank you."

;)