Some things - and on some people - just blur the lines between male and female. Take these tennis players:
Is Feliciano Lopez's butt feminine?

How about Rafael Nadal's?

Even his trainer probably doesn't know for sure

Maybe there's something in the water that rains in Spain; excessive growth due to gluteal warming, perhaps?
I've always found Serena Williams's booty a boyish eye-ful

Butt it's the other parts that no longer interest me.
Maybe what we need is a butt-o-meter with a Kinsey scale.