Beyond the more mundane ones like not knowing castling or en passant, I once knew a person who told me that one cannot promote to a second queen because it's bigamy, and I once knew a person who insisted that one must say "guard" any time a queen is threatened.

What humorous experiences have you had in this vein?

This happened 20 years ago and it still makes me laugh. I played a person who believed the queen was able to fly over the board and land on any empty square (or capture an opponent's piece)!

I have heard of this but it has been sooo long ago that I forgot the reference.  Until today I had forgotten what the word was.

It is called "en garde" and is French and means take care, I think it is a good way to help a weaker player and I often use it while playing with friends.

I was aware it was an old custom and nicety, but this guy had elevated it to a rule. If an opponent threatened his queen without saying anything, he'd invariably say, in a slightly annoyed tone, "you're supposed to say 'guard' when when you attack the queen".

Just kind of funny.