It's time to open this can of worms.

I want to unify the tags groping and fondling. This is because I find those words too subjective and because they basically mean the same thing. (dictionary: "feel or fondle (someone) for sexual pleasure, especially against their will." and "stroke or caress lovingly or erotically.". I crossed out parts that cannot be proven using TWYS. The distinction between "feeling", "fondling", "stroking" and "caressing" also cannot be proven using TWYS on a still image)

But first, let's start from the top, and define some useful terms.

Define sexual_interaction! In my opinion, it would be best described as, direct or indirect sexual touching (feeling/rubbing/stroking/.. etc).

When is touching sexual? I don't know, you guys tell me! But I think that touching is sexual when it involves sexy_parts (couldn't think of a better name atm). There might be some kinks depending on whether sexy_parts are the ones being touched, or if they're the ones doing the touching. Also there's some problems with butt and breasts as not all types of touching those could be considered sexual. Or could it. A girl touching her breasts.. hmm.. interesting!

What are sexy_parts? They are genitalia, breasts and butt.

What is genitalia? They are penis, pussy, balls. (I'm not sure about cloaca *grumbles*). Is there anything else down there?

Ok. So..

Enter groping and fondling!

groping wiki says, "sexual touching using hands". So basically, hands_sexually_interracting_something. That something is obviously in sexy_parts, otherwise it wouldn't be a sexual interaction.
fondling wiki says nothing. It's just an umbrella tag for ball_fondling and breast_fondling.
ball_fondling is currently defined as "sexually touching balls". So sexually_interracting_with_balls
breast_fondling is currently defined as "sexually touching breasts". Or sexually_interracting_with_breasts

And now for the grand solution!

I was thinking of using the word touching or rubbing so..

touching -> define as (always) sexual interaction between two characters or a character with itself.
groping -> hands_touching -> imply touching
ball_fondling -> touching_balls -> imply touching
breast_fondling -> touching_breasts -> imply touching

So. My solution is stupid. Now you guys post your solutions.

"touching" really isn't the proper term, it is so much ample and use it as a sexual tag can be confusing.

The word fondling technically comprehend groping too, so, I think that fondling should be used for both.