Is it really necessary to say that all men have short hair? That's... not even nearly true enough to be worth mentioning. Besides the fact that throughout time and different cultures, long hair for men has been normal in as many places as not, in modern Western cultures, chin-length hair is considered gender-conforming for men (example, Lelouch) and that's still long enough for a clipping to be substantial.
Is it really necessary to say that all men have short hair? That's... not even nearly true enough to be worth mentioning. Besides the fact that throughout time and different cultures, long hair for men has been normal in as many places as not, in modern Western cultures, chin-length hair is considered gender-conforming for men (example, Lelouch) and that's still long enough for a clipping to be substantial.