What is a face mask?
This isn't a rhetorical question. The face_mask tag is an ambiguous undefined mess, and the term "face mask" itself doesn't convey any information other than that it's a mask that's worn on one's face, which is the case with all masks anyway. The term is so vague that Wikipedia even lists "diving mask" as one of its possible meanings. Dictionary.com gives a different definition altogether.
The vast majority of posts with this tag should have been tagged either ninja_mask, surgical_mask, or gas_mask. The rest are a veritable grab-bag of face coverings that aren't even all masks. You don't have to look too hard to find loads and loads of posts that confirm this. Just browsing through these posts, I see domino masks, fox masks, half masks, noh masks, masquerade masks, wrestling masks, balaclavas, blindfolds, helmets, and veils. They're all over the place.
Creating an implication to a tag that doesn't even have a definition in the wiki is something we should never, ever do. Come up with a clear definition for the tag first; talk about implications later. As it stands right now, my vote would be to nuke face_mask entirely because so many users are habitually treating it as a catchall tag that is redundant to mask.