The sexual act consisting of 2 men naked, a cup full of shit, and a large dildo. One man shits into a cup while the other man gets into doggy-style position. The man who has now shat in the cup sits on the other man's back, riding him like a horse while holding the cup full of shit over the other man's mouth and nose. The man on top also fucks the bottom guy in the ass with the large dildo, completing the "Iron Horse" This is an example of a dusty poo fetish, and can also be seen at gay orgy's.
Guy 1: Man after you gave me that iron horse I will be blowing shit out of my nose for weeks!
Guy 2: Not to mention your ass will be sore as hell!