True crime shows used primarily by middle aged couples to get aroused. This phrase was coined by South Park in the season 17 episode of the same name.
Randy:"What is Minecraft, and how do you tame a horse in it?"
Stan:"You guys don't need to be watching that stuff."
Randy:"Oh come on! You can't block your parents from watching informative murder porn!"
Murderhorn is what most people would consider an oversized cock. Note: This also pertains to anything that's larger than the "middle ground" of the average sized dude.
Jenny: Wei is small as fuck. I think my ass cheeks are deeper than his 5 inch cock.
Lindy: Didn't you know that Wei actually means "Way Small?"
Jenny: No I didn't, but now I do.
Jeremy: I have a 6-1/2 inch cock.
Jenny: Not bad.
Amanda: But any cock over 7 inches is a MURDERHORN.