To masturbate or to be masturbated or to be given a blow job. As heard in the Katy Perry song, "California Gurls".

In some kid friendly performances, she will say "melt" i.e.: the today show, where it is obvious what she is saying.
However, in other performances i.e.:SNL, it will be more obvious that she is actually saying "milk" and will accompany the line with a hand jerking motion.
In the video she pops her cheek to suggest a blow-job.

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.