It’s not a compliment to be called mechutzaf, but it is not the worsrt insult ever, either. It’s very simple, if you are called that by someone, I would try and examine my words or actions to see why someone believes I spoke or acted in a nervy way. Apikores is not a Yiddish word in origin, though I am sure people who are speaking Yiddish have referred to someone as an Apikores. Not every Hebrew word has ane xact English equivalent. The word “es” comes to mind, as in “Breishis Bara Elokim es HaShamaying v’es haaretz.” The Torah could have easily simply said, “Breishis Bara Elokin haShamayim v’haaretz. The presence of the word es comes to denote that there is something extra that came from Brias Haolam, but it does not mean the actual word “extra.” Sometimes “es” means “with” in a different context, but that is not its typical meaning.
I did not read the thread in which you feel you were castigated (and probably will not now). As to Apikores, perhaps it is Aramaic, perhaps Greek (from the same word Epicurean?). I do not believe it originates in Hebrew. It basically means someone who denies the Torah or a portion of it, as not being Divinely Written. Mods, am I right about this?