An extremely boring person, who still thinks they’re cool or worth something
They make groups to make friends and hook up with younger people. His group members are horny teenagers, or toxic.

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.