Yeah I think this is a thing of the old days, my father in law is also always on top of light usage. Once I calculated what a 3W led cost him if he let it run the whole year (about 6€) to forget it once in a while is really no reason to get cranky. Leaving a couple of 60W incandescent bulbs on for longer periods can increase a bill indeed, but with leds it’s really not worth being know as the guy that whines about the lights for, IMO.

I don’t really think it’s about cost for these people. There’s something about a needlessly glowing lightbulb that is just offensive to them.

Well, I agree that lights should just be turned off when not needed, it also kills their lifespan. But you don't have to be a nasty person about it :)