I just walk in front of them, interrupting their set, and grab whatever weight I need. I don't even bother with an "excuse me". They learn quickly, after the second interruption.
Man, lifters like *you* annoy me. You go to the gym to lift weights and then complain that working in with someone who uses lighter weights than you means you have to... omfg.. move heavy plates around? If your gym had an escalator and stairs, I'd bet you'd take the escalator. I don't mind a skinny dude working in with me, because every time I mount and unmount plates I turn it into a goblet squat, bicep curl or front plate raise.
I have my ear phones in and can't hear shit, so talkers and grunters don't disturb me. And you know what? Who gives a flying fuck what other people think of themselves. Mr 19-inch fatty fat arms doesn't affect my workout, neither does the guy walking around with Imaginary Lat Syndrome. The only things that annoy me are smells, and things that directly affect my workout.