A complex of behaviors which are characteristic of and natural to a man, and the direct result of male biology.
Men are by nature active and aggressive, and a man naturally expresses his sexuality through the thrusting of his erect penis -- his phallus.
Male sexuality then is expressed phallically.
Being penetrated anally has never been natural or appropriate to a man and never will be.
Again: Masculinity is that which is natural to a man.
Male sexuality is expressed phallically, in the way which is natural to a man.
Thus our Man2Man Alliance formulation:
Manhood is Man
See also Frot, Natural male sex aggression, Sexual dimorphism, Natural masculinity.