In my experience, whenever a female friend has returned an unwashed shirt borrowed for some reason, the shirt always seems basically clean, even if returned with apologies that it was profusely sweated in.
Now when I wear a shirt for a day, it's dirty.
And if I loan a shirt to a man, I'm basically loath to touch it at all before getting it into the wash. And the thought of just throwing it away is never far from mind.
Because I know how ripe I get, but at least it's MY ripeness.