TBH in the past, I've argued both for the -um ending, and for the -ium ending. It really annoys some people. It's even more annoying, when they realise that you've managed to annoy them with such a pedantic point.

Another one is skeptical/sceptical. "I think you'll find it comes from the Greek, so it should be with a k."

Or the plural octopus. "I think you'll find it comes from the Greek, so it's octopodes. Octopi is certainly wrong, because it doesn't come from latin."

I think I may be an energy vampire.