Sassy, sexy pop from divas and weirdoes spanning the last four decades and this whole beautiful, crazy world.. In a defiantly campy neighborhood, Medium Rare may have more camp per square inch than any place except Castro Street itself on Halloween. Since 1991, the small, tidy shop has celebrated the work of divas, egotists and pop extremists of all stripes. You never know what oddity will assault your tender ears when you step inside. Check out the wall of glam promo pics on the back wall for fashion dos and don'ts. The unifying theme of Medium Rare music -- its slogan is "where everything is well done" -- seems to be artists who truly gave their all. Gay icons like Liza Minnelli, Judy Garland and Peggy Lee are represented, as are '60s girl group cuties, teen idols, Francophone lounge exoticists like Serge Gainsbourg and Jacques Brel, soundtracks to''60s gems, novelty nuts like grandmotherly rocker Mrs. Miller and forgotten new-wave genius Klaus Nomi. The extensive stock also includes plenty of imports and rarities.…