A combination of the words weeaboo (extreme anime fan/Japanophile) and derp (stupid or ignorant person).

Basically...it's used to describe a very stupid anime extremist.

Despite what some people think, there is a bit of a difference between a weeaboo and and a weeaderp.

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.