If you’re thinking about becoming a GM, I cannot recommend enough Justin Alexander’s (of The Alexandrian fame) new book So You Want To Be a Game Master. It’s a really great step-by-step hand holding guide that we probably all wish we had growing up, or that the DMs Guide actually provided but doesn’t (yet?)
His whole website is full of practical tips for the more advanced GM as well.
The origin is he was called a “short fingered vulgarian” in a print article in Spy (which called Kissinger a socialite war criminal). It means that he is cheap (short fingers don’t reach deep into pockets to get at money) which he took literally to mean having small hands. Dude just slid right past the actual insult and moved on to a different one that he either preferred to argue against or substituted because he didn’t understand the original.