go medieval

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.

Refers to an upcoming violent behaviour on somebody's ass. Medieval civilisation is known for it's cruelty and violence, therefore when going medieval on someone, the results can be truly devastating.

beat/beating the living hell out of somebody, either physically, or mentally

also known as "kick the shit out of"

to lose one's temper on, to lose one's emotional equilibrium and act cruel or savage to somebody