“Chopped unc” is slang, especially in the United States.

unc = “uncle,” usually referring to an older guy or someone who acts old.

chopped = unattractive / not good-looking.

So “a chopped unc” basically means an unattractive older dude, often said jokingly or as an insult. 😭

(http://www.autoadmit.com/thread.php?thread_id=5893075&forum_id=2/#50067680)