two meanings. In (very loose) medical terms it refers to anal warts, hence the word 'shit'. In slang it refers to an irritating bastard who needs a good kicking. The actual slang word is a play on the insult 'Dickwart'

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.