As a Marine (got out many years ago), most of us don't give a shit. Some did while they were active duty, but it was only when other people brought it up to get a reaction from the Marine. There are still some loud Marines that would say something just to be loud. We come in different flavors of annoying.

While I was recruiting, I was called a soldier by a few teachers and parents and it doesn't matter. What matters (to me) is the intent, most people are making an honest mistake. Some are trying to get a reaction out of you, I might respond if it was a bit friendly, but I mostly ignore it.

Being called a Marine instead of a soldier, is part of the brain washing. It helps point to something and say "That's why we are better. Marine is a proper name and should be capitalized. Also don't put your hands in your pockets. That for the nasty Army to do and not the Marines. We get held to a higher standard."