I just realized as I was posting this that there is a model for this but I trained this one on 3 variations so I still think it has merit. The variations are just the tips touching(penikiss), shafts crossed(swordfight), and shaft touching shaft(shaft2shaft). Real simple tagging here.
Example Prompt:
frottage, 2girls, futanari, dark_skin, penikiss, sitting, blush, gloves, wet_clothes, wet_shirt, white_gloves, ponytail, small_breasts,
FYI as per usual this dataset contains zero men so if it works for men, great but I'm not testing for it.
Description
If you are having trouble generating the correct style of frottage then try omitting "frottage". It sounds silly but it seemed to work for me.