Well then say that MacOS is 3 pixels slimmer than Mac OS but it just doesn't have the same feel and I'm constanly get crumbs stuck between the c and the O.
I personally just say Mac OS. If there were some device called the Blarg, with an operating system built to run just on the Blarg, then that operating system would be most naturally called Blarg OS; I suspect the vast majority of people would call it that if no name were supplied.