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When one heterosexual man (Man A) runs up behind another (Man B) , jumps, pushes of the Man B's shoulders, and humps the Man B as high up on his back as possible. This is usually done to show Man A's dominance over Man B, or to make Man B subservient.
Rob: Dammit Steve! Quit Man Humping me! It's annoying as hell!

Steve: Maybe I would if you weren't such a little bitch.
by Nicky Nick and The Funky Bunch October 18, 2009
When two fully clothed (non) gay men kiss and frolick with one another in a public display of animalistic psuedo-affection.
Chris got so liquored last night he attacked that unsuspecting fellow in the soft hat and started man humping him on the ground.
by Bellinger November 12, 2006