Experience. It is the best teacher after all. Don't particularly care whether people believe me or not. I own half a dozen horny streams that numerous people constantly report. Over the years, seeing what sticks and talking to global mods about why, has yielded the above findings. It is by no means exhaustive, but covers about 95% of contentious issues.
Among the things I don't yet know is why in the name of Zeus's ballsack none of this appears in the no nudity rule. š«¤