I am of the opinion that this tag "no ass" is largely subjective and, even at only fifty-five occurrences, overused. What can be done, if anything?

Hmm, it does seem like this tag is really unnecessary.

I don't see what makes it any less necessary than tags like veiny_penis or thigh_gap. "No ass" seems to be a bit of a misnomer, though. I'd advocate replacing it with small_ass or flat_ass.

On Danby there are penis depictions which show some vein and others which just don't. There are also many pictures of legs and thighs which do and do not concentrate on thigh gap. However, there are no ass depictions which correctly display "no ass."

Your suggestion to replace tags makes sense.

Aliased to flat_ass, sounds better.