An REMF is an officer who is likely a great staff officer, but should never be allowed near soldiers in combat units. I was Air Defense Artillery for 8 years, and I bristled when I came into contact with staff officers trying to tell me the right way to do things.
I had a couple of commanders who were REMFs, they never let us Platoon Leaders do our jobs. All 4 of us were damn good, too.
LOL, I have indeed heard that one before. Used in the most derisive of ways by people who are entitled to use it, it can sure cut deeply.