Just how in the hell could I know about your freemason secret
handshake?

Well, it's not a secret! If it were secret I wouldn't share it with my own
mother, much less air it on Usenet. But that is the whole point of the term.
It is (to most people anyway) an unoffensive question which, at worst, might
seem a bit odd. To another Mason, the question is usually immediately
understood.