(as) mean as a junkyard dog

(as) mean as a junkyard dog

Exceptionally cruel, spiteful, malicious, or violent. Her dad is usually a pretty nice, chilled out guy, but he's gets as mean a junkyard dog when he's been drinking. Don't go messing with that guy! He's mean as a junkyard dog—he'll rip your head off just for looking at him funny!
See also: dog, junkyard, mean