Proving he can roll with the ladies-who-lunch set, chart-topper Nelly drops accessory knowledge on a young ''shorty'' in his recent single ''Flap Your Wings.'' He gives a shout-out to Judith Leiber, the now-retired 84-year-old handbag designer. While Leiber's signature crystal-encrusted purses have long been a red-carpet staple for A-listers like Renée Zellweger, Nicole Kidman, and Sarah Jessica Parker, the Nelly name-check gave the posh bags street cred. In return, the company has custom-made Nelly a monogrammed alligator case for his beloved Sidekick PDA; according to CEO Maggy Siegel, it's ''the first product that we've ever made for a guy.'' Holla!