I'm sure you are right and probably most people mean well. The issue is usually mine. But, for whatever reason my mind just goes there. Which is why it usually safest for me to just smile and say thanks. Nothing more. Nothing less.
Just last night my hubby made such a comment about my butt and he knows me well enough to know how I heard it...so he was really trying to say it the right way. The only thing I said to him was "Really?" In my mind, he was just wanting some of my attention if you KWIM. For me, he would have done better to never mention the specific body part and just say I can see you are losing or something like that. Poor guy...he can't win and he was trying hard.