I am curious, how do Marines react when another branch calls them "Gunny"?

We had Marines as instructors and students in weather tech school. The Gunnery Sergeants were perfectly fine with being called Gunny. The problem as others have said is referring to anyone with more than three stripes as a Sergeant. The reason being Sergeant is a specific rank therefor calling anyone else a Sergeant is essentially demoting them. I am not sure why the Army isn't the same, I guess they are just a little more laid back.