One very easy example to show that sexiness is indeed übersubjective: Orlando Bloom.
Girls swoon over that guy, and I honestly don't get what it is they see. Judging from the Orlando Bloom love/hate thread we had on KKW sometime, I'm not the only girl who thinks he's pretty average, yet others are convinced he is the definition of sexy. If there is indeed a blueprint for sexy; all girls on the planet would have to agree on the (lack of) sexiness of Mr I Was Pretty Good In LOTR As Long As I Didn't Speak. Not the case.