Mangy means patchy-furred and shabby, like a stray with a skin disease. Bald in places, and not well.
It comes from mange, a genuine parasitic skin condition in animals caused by mites, which produces exactly that patchy loss of fur. Applied loosely it means shabby, so a mangy old coat is one that has lost its nap. It is always disparaging. Foxes with mange are a common sight in British towns and the condition is treatable, which is worth knowing before assuming the worst.
1adjectivemangyHaving patchy fur from disease, or shabby and worn.
“A mangy fox crossed the road in front of them.”
Also accepted in games: scruffy
From mange + -y.
Etymology from Wiktionary, CC BY-SA