I feel that a topic for commonly misused tags would be useful to have since I've seen some tags being frequently misused despite clear notes on situations NOT to use them in. It will at least make future tag cleanups slightly easier and not clutter up topic #12251.
If you happen to encounter some commonly misused tags or tag combinations, please bring them up. I'll put the ones I've noticed to start with.
crescent_moon for crescent shaped objects/symbols. This was/is common on characters like patchouli_knowledge when it should have used crescent_hair_ornament or just crescent instead. This is a rather annoying tag to clean up because crescent_moon implicates moon, which means two tags need to be removed or else there will be images of characters in broad, moonless, daylight tagged with moon.
facing_viewer is to be used on characters with closed eyes. If a solo image contains both facing_viewer and looking_at_viewer, something has been tagged wrong or the character tagged is a special case (Like, say, an Ettin-chan or something).
floating (when on air) instead of afloat (when in/on water). This is an understandable mistagging due to the very similar circumstances of both tags, but it's not an easily cleaned one due to the need to judge them case by case. In any case, searching floating and water will result in images that need afloat instead but also images where a character is floating midair above water.