Ah... No mate, there are no "somethings" for "most countries". Most of the world uses straight up metric and that's it. What "local systems" do you know of that get used alongside metric?

And regarding the grow up part... See, here in Europe everybody will crack jokes about everybody else. French laugh at Germans, Polish mock the Spanish and everyone laughs at the British because they can't come back at us since they had their little voting oopsie and now need a form to import jokes into the EU.

Remember that one kid that never got the joke, took what was said in jest at face value, got upset and thus mocked even more? Americans have a surprising tendency to be that kid.