I cant answer your question but maybe the best example you could use is female dog ie ***** (and I am using it scientifically! which has just turned into a bad word, with people using it incorrectly!
As fo s**t - I think thats just a swear word. No good on that one!
It is amazing how words change over time! Years ago if someone was "naughty" they were referring to criminals!
IMO curse words are stupid. What's the difference between me saying "darn it" and "damn it"? They carry the same meaning, but one is "bad" and the other is "ok". I think that all words should be ok to use as long as you're not using them to demean someone. It should be ok for someone to say "F*** this" if they're frustrated, but not ok to tell someone "F*** you". Calling someone stupid is far worse than saying "oh s***" IMO, but stupid isn't a bad word.