also: げすやろう
noun
sleazebag; asshole; lowlife
Strong derogatory insult for a contemptible, vulgar, or morally repulsive person. Rough and offensive; used mainly in casual, angry, or vulgar speech.
あのゲス野郎、また嘘つきやがった。
That sleazebag lied again.
ゲス野郎には関わりたくない。
I don't want anything to do with that lowlife.
クズ is a common insult meaning 'scum' or 'trash', often used for worthless people. ゲス野郎 is more specifically about vulgar, sleazy behavior and carries a stronger tone of personal disgust.
野郎 alone is a rough, derogatory term for a man ('bastard', 'jerk'). ゲス野郎 intensifies it by adding ゲス (vulgar/low), making it a harsher insult.
Compound of ゲス (vulgar, low, sleazy) and 野郎 (rough term for a man). ゲス is often written in katakana in this compound; its origin is uncertain but may be related to 下衆 (げす, 'low-class person').