When one farts so much in one day (without starting) that a thin tarry film is created on ones underwear

A phrase to describe someone who is cognitively degenerating. Synonym of "going off the deep end". Can have varying degrees of severity.

Reference to the song "Hey You" by Pink Floyd. The line "and the worms ate into his brain" makes no sense in an otherwise linear and literal narration throughout the lyrics.

To fart so much in one day or between changing of underwear (without starting) that a thin tarry black film of shitty residue is president on ones underwear.