There was a man named Grim, nicknamed Hairy-Cheek because he was born with a certain peculiarity, and this is how it happened: When Grim's father, Ketil Trout, went to bed with Hrafnhild Bruni's-Daughter, her father Bruni spread a hide over them because he'd invited a number of Lapps in. During the night Hrafnhild happened to look out from under the hide and caught a glimpse of one of the Lapps who was hairy all over. That was how Grim got this mark: for people think he was conceived at that very moment.
- Arrow-Odd, (Anon. 13th century AD)
OK, so I know that Lapps are really just people from northern Scandinavia, but let's D&D this up a bit. Lapplings are small hairy fae creatures, related to brownies, but more suited to colder climates. They can craft finely detailed objects with their tiny hands, and for this reason men will sometimes welcome them as trade partners. However, it is well known that lapplings are mischievous and should not be allowed to stay in a human camp or town for too long.
The strangest property of the lapplings is this: that if any woman looks upon a lappling at the moment she is conceiving a child, then that child will be born with thick hair growing somewhere unusual on his body. Powerful lappling chiefs may produce children with hair all over. The lapplings do not gain any real benefit from this, but they find it so amusing that they are always trying to sneak into bedrooms at the opportune moment.
There are several things you could do with lapplings. The PCs could be hired to get rid of a lappling infestation, or the patch of hair could be a distinguishing feature of an NPC. What I would really like to do, though, is wait until one of my PCs is having sex (admittedly this doesn't come up very often in the course of normal D&D play) and then have a lappling creep up on them.