It's always surprising to me that there's a lot of words that, to the best of my knowledge, are not someone's surname. Like Doe. How could a simple word like Doe not be someone's name? It seems like it's not a name but then can stand for the generic name, John and Jane Doe. How is that possible?
Then there are the words that stand for something else but never made the switch (or stood prior to common usage). Like Undies. That's the nickname for underwear, a diminutive word, like Fundies for fundamentalists.
I've never met anyone named Undies, for either a last or first name.
But if you had someone, of course the kids in school (me included, regrettably) would've had a field day with it, until the novelty wore off.
Theodore Undies, nicknamed "Dirty."