a man seeing that someone he knows might be getting it on with a nice looking lady, waits for him to head to the toilet or the bar and then swoops in to take that lady for his own.

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.