That layer of odor in shoes or other frequently-worn article of clothing that remains no matter how much you air it out.
Like permafrost in the Antarctic, only with stench.
Also: permafunky, permafunked
T: Honey, it's time for a new pair of slippers.
M: But why? They're comfortable!
T: Remember when Woofie would bring them to you every night?
M: Yeah. Good times.
T: He buried them today. The permafunk was too much even for him.