Green’s Dictionary of Slang

medieval adj.

[the stereotype of the Middle Ages as symptomatic of such excesses; the phr. was coined in the Quentin Tarantino film Pulp Fiction (1993)]

In phrases

get medieval on someone’s ass (v.) (also get medieval on someone’s arse)

to treat with extreme savagery.

Show quotations
[US]Tarantino & Avery Pulp Fiction [film script] 108: Hear me talkin’ hillbilly boy?! [...] I’m gonna git Medieval on your ass.
[UK]Observer Mag. 22 Aug. 14: At least until Kathy Bates got medieval on his ankles in Misery.
[UK]T. Pratchett Truth 149: An’ then ... then I’ gonna get medieval on his arse.