Pornography depicting and directly involving equine.
An exclamation used in situations similar to "fuck!" intended to arouse a greater amount of shock among audiences. Great for surprising nearby folks and making them feel akward.
Also can be used to describe something as being BS or meaningless
Person 1: Dude, there was gum on that bench you just sat on.
Person 2: Aw, Horseporn!
Person 1: I just aced my chemistry exam!
Person 2: What? Like hell you did, that's horseporn!