I can’t believe I’m the first to mention that The Second Stone actually fucked up the joke.
The original insult, from Full Metal Jacket, is “It looks like the best part of you ran down the crack of your mama’s ass and ended up as a brown stain on the mattress.” Said, of course, by GSGT Hartman. The implication being, that the subject of the insult began his existence as a small bit of semen, which was separated from the greater mass of semen (the “best part”) ejaculated by his father, the latter of which slid down the crack of his mama’s ass, thereby mixing with shit, and ultimately ending up as a brown stain on the mattress.
The way The Second Stone told the joke, he said “a brown stain running down the crack of his mama’s ass.” But that doesn’t make sense. A stain doesn’t move, it doesn’t run down anything - a stain just sits there. A stain is what is left after “the best part of him” runs down the crack of his mama’s ass.
In other words, the logic of the insult, in this retelling, is deeply distorted.
Well I am an idiot and doing it from memory. Here is a not entirely safe for work soundboard you can play in the background during phone calls. Note, take out the extra spaces, I don’t want anyone clicking on it accidentally.