Why do so many men hate other men with waist-length long hair?

Basically my friend that has waist length hair get called slurs and the like whenever he speak to people my age/gender and i have no idea why. My hair is eye length and wavy and my face isn't particularly masculine or femenine. But, does anyone know why men hate men that have waist length hair? As for women some also dislike men that have waist length hair whereas some women actually love men that have waist length hair.

Why do so many men hate other men with waist-length long hair?
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