at minimum female nipples go straight to erotica because it's almost always sexual.
No,that's not true.
Suggestive is where nipples alone go,the absolute maximum that suggestive has,since just showing nipples alone is common in a lot of comics where nothing further happens beyond that on screen.
Same with two(or more)characters about to get their Dues Vult on in the bedroom and then the scene progressing straight to the aftermath.
Erotica is when they actually start getting it on like Donkey Kong on screen or they start showing the lower half with barely anything to stop it being viewed.
Pronographic is when they start shakin' the bed with the gonads exposed in almost clear detail or uncensored lower halfs,like what happened with the understanding girlfriend series when the newest scanlator uploaded the uncensored Fanbox content.