Saying the wrong thing at the wrong time

My sweet David let me know that my tummy was fat yesterday. I looked at him and let him know that most people don't like it when you mention they are fat. And most people who are fat already know they are, so they don't need a reminder. That said he looked at me with a sweet face trying to figure out a way to say something nice about me in a way that didn't call me fat. He first said "I like . . . your . . . whatever. . ." Then he came up to me and pointed to my arm and then my thigh and said "I like these parts on you mommy because they are soft" I hugged him and kissed him and said that was much nicer then calling me fat.

David's my kid who blurts out what he thinks. A little like his Dad in that aspect. On Easter Sunday we had a delicious leg of lamb with parsley potatoes and steamed broccoli. We also invited two families from church. Each brought yummy fruit salads. One had cool whip in it. While David was at the table with the kids he says very loudly "Jack, don't eat this one it's disgusting" Unfortunately the maker of it was sitting right beside him. I hoped that she didn't hear because she didn't show any signs of it and it was a little crazy as kids were dishing up stuff. I liked it and made sure to tell her on the way out how good it was. I later had a talk with David on the etiquette of being polite when you don't like something. He will also loudly point out at the store when he sees someone with piercings or tattoos or immodest clothing. Sometimes people hear him and I hope most the time they don't.

Any ideas on teaching little kids tact?