Implicating cum_on_nipples → nipples
Link to implication

Reason:

EDIT: Oh wait. I see what you're meaning. 'cum_on_nipples' requires that there are 'nipples' in the post; however, 'nipples' is meant to differentiate Safe For Work posts tagged 'female breasts' . Adversely, this may be too specific as 'cum_on_breasts nipples -rating:safe' search string may be feasible.
There are currently 159pages of 'cum_on_breasts rating:explicit'; there are 1pages of 'cum_on_breasts -rating:explicit'; there are 152pages of 'cum_on_nipples';.
*There are currently 159pages of 'cum_on_breasts' where the 'nipples' tag is applicable, but missing'.*

This is the other way around from what I'd thought. Ignore the original. There is an issue of efficiency between search strings 'cum_on_breasts nipples -rating:safe' ; 'cum_on_nipples nipples -rating:safe' and 'cum_on_nipples clothed +/-rating:safe' if the tag 'nipples' were associated with 'cum_on_nipples'.
There may be an easy resolution, but my brain has just exploded so I digress.
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ORIGINAL
_positive reinforcement_
IMO easily resolved by 'cum_on_nipples' alias 'paizuri'. Otherwise, just 'cum' . IMO what it is on is thus far irrelevant as half or less results may show it not in contact with skin, fur, scales, chitin, etc.
-negative reinforcement_
Shame! Avoid 'cum_on_nipples' tag. Tags like 'creampie' and others have a specific meaning, they perpetuate specificity and require specificity. IMO we do not need this specific tag yet. IMO 'cum_on_nipples' is not a useful tag unless there are hundreds of posts where it is the focus(IE it is centered on the action and takes up more than 40% of the viewable area). *There are currently 152posts* with this tag, IMO that is not enough unless they all follow a focus on the action.
I would avoid it for now in favor of a user effort to get what they want in the search like the string '{1boy/1girl} -creampie cum -faceshot'. That may be a little too specific of a string, but that would be a round about way of finding similar items to 'cum_on_breasts'.

Do we really have such tag? I'm going to create a cum_on_pinkie_finger tag.

Lizardite said:
Do we really have such tag? I'm going to create a cum_on_pinkie_finger tag.

There was some talk about pruning the less common ones, but that got nowhere.
So if we are going to keep them, then might as well implicate them to make tagging a bit easier.