Phoebe has some interesting thoughts on the elusiveness of flattering clothes: in particular, how the very secondary sex characteristics that appeal to the "Darwinian hindbrain" make clothes unflattering.
To relate this back to Lady Gaga: Part of why her spectacle is so compelling is that she's completely short-circuited the frump/skank dynamic. It can be startling to see a scantily clad pop star who is so emphatically not seeking your approval through the standard channels to sex-object status. Is this really skanky? Frumpy? There's something almost wholesome about her here, like a diving girl from a century ago. And a lot of the time she's embracing the iconography of sexiness without actually submitting herself for your sexual assessment or gratification. The refusal to submit was particularly marked during her performance of Teeth---Gaga was definitely the sexual subject, and the audience was getting the business.