"Look at that old bag o' bones over there. She's really festered out."
Broken down; out of commission, on the fritz.
"What happened to your car Sally? Oh, it's festered out again. I think my hubcaps are bad."
What happens to a large pimple with a big white head that grows in the middle of your back that you can't get to.
"Dan what the hell's that on your back? It's all festered out."