What is the worst thing you can say to a new mom?

There are a lot of things that you shouldn't say to someone who's just given birth. For example, never say "What do you do all day?" That's a universal rule for all new fathers. Never give unsolicited baby-care advice. This, combined with the hormones, would turn me into a raving mad woman. "I know how to take care of my own baby," I'd yell at my husband.
But definitely the worst thing you can say to a new mom: My husband came home from work one day, two months after I had given birth. We were sitting down and eating dinner and talking about our days. Then he said, "You know, Jamie Lynne Spears already lost her baby weight. Can you believe that?" It took everything inside of me to not throw the water glass at his head. I still get angry about it on a weekly if not daily basis.