The number one ranking emetic phrases that refer to sex have a fraud has been perpetuated in time for the nerds that make strange faces can procreate without having to merit it.
The phrase itself is a stupid analogy based on the shape of the instrument that prefer to avoid, for obvious reasons, saxophonists, bagpipers, flutists and trumpeters.
Apart, of course, leave the machismo prehistoric Bingueros gooey and oozing this wonder of the lore. Translated
to modern Castilian, this expression amounts to saying: "These trained fingers touch your right spots, we apply a slight vibrato and if I see that it costs me and I put a capo on the mast."
To our misfortune, the guitars never say "no."