Maybe it's the inherent domination of the one over the submissive on his knees. I remember reading once about some ancient race, perhaps the Greeks, who after winning a battle sometimes demanded their captives kneel and suck their cocks. Now that's hot.
I've also heard tell that some fraternity houses require new pledges to kneel and suck the upper classmen's cocks in a secret ceremony. Others have told me that's complete bollocks. Even if it is, the image in my head is still vivid.
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