The story
From get (“to become”) + medieval (“relating to medieval dungeon torture methods”); originally merely collocational when attested in the dialogue of the 1994 film Pulp Fiction, but the collocation took on the function of a phrasal verb, entering the lexicon as a term for torturing severely, after it went viral as a consequence of the film's popularity.
Etymology from Wiktionary, CC BY-SA 4.0.