As for flip flops..... I say Burn them! Burn them all, burn them now, and burn them fast! Take the ashes out into the desert, and bury them in deepest hole you ca possibly dig!!!!
HOWEVER...... I believe the original intent of this post is in reference to hiding toenail polish in an open sandal of some kind, or even a bear footed beach. Personally, I don't worry about it. Besides, male toenail polish has become an accepted thing among hipsters. Si don't sweat it this summer! (pun intended) and go out and about in your open footwear with your fresh clean peddi