Eight Weeks, by dwimordene_2011. In which Boromir tries to grow a beard, and Denethor and Faramir join forces to convince him of the wisdom of shaving it off. A very cute (and quick) read that's always worth revisiting.
I have vague memories that there was a community in the Tolkien fandom that had these wonderful debates every now and then, about whether Numenoreans and Dunedain would or even could grow beards. Also about someone who had rather involved theories about how you could ever have women who weren't hormonally a mess but could still grow a full beard capable of being mistaken for men. Dwarvish men at that. Seems like there should be other nice fics about beards in Ardaverse, but I can't remember any at the moment. Does anyone else have any worth mentioning?