Long hair! It's feminine. Most guys would probably say they like dresses on girls, heels, and of course boobs to name a few. Regardless of whether one of these features is a social construct or something biological, straight men are for the most part attracted to feminine things simply because they are different from us, a little strange/mysterious, and associated with the opposite sex. Most girls would probably say they prefer short hair on men, a little musculature, and would die for a handsome man in a suit. That's only speaking generally of course, we all have preferences and these things aren't rigidly defined. A very "masculine" man can have long hair (a la Fabio *sniggers*).