Then add tags for the others. (hyperbolic) It's not like they can't exist, they're not opinions and they hurt no one. Being added by one or two people isn't a reason to dismiss them when they're not opinions. You have to look at it like that. If you see a tag that you suspect is a waste of time, ask yourself, if it an opinion, or is it a fact? Rarity's dress is a fact.
Imo I'd just rename it to remove her name so it can serve a universal purpose, but staying just for her isn't hurting anyone either. It can prove useful and isn't bogging down the tags with opinions like 'sexy'.