The way most of the world's people experience sex: through the contact of genital tissue with genital tissue.
For "heterosexuals," genital-genital sex is penile-vaginal sex.
For men who have sex with men (MSM), genital-genital sex is penile-penile sex: Frot.
There are no other sex acts available to MSM which consist of direct genital on genital contact, and which provide the instantaneous and intense mutually phallic feedback of Frot.
Which is why no other m2m sex act is as powerful.
As Warrior Don F says,
I want to have sex with a buddy's MALE anatomy mated to mine.
Just being anti-anal is not enough----we need to emphasize the sensory feedback loop achieved through anatomical coupling, stimulating each other's genitals naturally so both buddies feel the same sensations at the same time. THAT is sexual intimacy.
And, it's an intimacy that leads guys to full and complete UNION, without BARRIERS between them so the natural male flow from their bodies is free and openly shared, unabridged by rubbers or any artificial containment.
It is a confirmation of masculinity.
In the Alliance we celebrate male sexuality as a pure, honest and instinctive expression between buds who can be GUYS together.
For a man and a woman, genital-genital sex is penile-vaginal intercourse.
For a man and a man, genital-genital sex is Frot.
Readers interested in a fuller exposition may read our very popular and adult article What Sex Is.