A filing cabinet is formal term for a person that exhibits little to no intelligence, provided that they have a functioning brain. Many people mistakenly use terms like "stupid", "retarded" or "mentally handicapped" in place of such a word, but those words are reserved for people without a fully functioning brain.
Flunch, derived from the similarly-named fast-food chain, "Flunch", is a noun which refers to the object of oral human expulsion (vomit), or a verb meaning to "to vomit".
The reason this word means "vomit" or "to vomit" is because the restaurant is absolutely revolting, serving up rotten mussels and frozen sweet products. After dining at the restaurant, if it can be justified as dining, we literally felt like vomiting, or flunching.