Buffy the Vampire Slayer (1997)

S4E5 Beer Bad

Xander secures a job as a bartender at a local pub, but chaos ensues when some of Buffy's acquaintances undergo a shocking transformation into fearsome Cro-Magnon beings after a night of heavy drinking. As the situation escalates, Xander must navigate the havoc and try to restore normalcy before it's too late.