Not more than a few humid seasons ago, the only guys wearing them were left-behind boomers and German tourists. Then came Tevas and flip-flops from J. Crew, and Russell Crowe in Gladiator; now you canít drop a drachma without hitting some air-conditioned footwear. Barneys covers the fashion waterfront with styles ranging from sporty (Camper, Miu Miu) to high-fashion (Gucci, Dries van Noten, Prada); Otto Tootsi Plohound (38 East 57th Street; 212-231-3199) gives you the street-style innovations from Yogi by Duffer, Pawelk, and Samsonite -- yes, Samsonite. But our favorites come from Cole Haan with its updating of Birkenstock classicism and its rustic attempt at converting men to wearing closed-toed mules. If itís a choice, however, between Greco-Roman eroticism and men in mules, we vote for Spartacus.