From the movie Pulp Fiction, one of the most feared characters stated his henchmen would "go medieval on yo' ass", which basically was a way of saying his men would click out on the men being threatened. To go medieval means to become savagely violent without restraint, similar to how we imagine those in the savage, unrestrained medieval times would respond to someone who had done them wrong.
Don't make me "go medieval on yo' ass!"
beat/beating the living hell out of somebody, either physically, or mentally
also known as "kicking the shit out of"
Look at me like that again and I'll go medieval all over your ass.