There are certain phrases that implicitly signal social faux pas to us, and one of the main ones I grew up with was "no discussion of sex, religion or politics" at the dinner table or with any people you did not know well. I recently repeated the phrase and found this sentiment is not universally known. From some googling, it does seem to actually be a 'thing,' but I'm finding it mainly mentioned in articles as conventional wisdom and am having trouble figuring out where the phrase/'rule' originated from. Any of you great folks have any insight?