I HATE the "he's so good" or "you're so lucky to have such a sweetie" or variations thereof! Not, mind you, "what good manners he has!" or "he's so polite" or "clearly mom has taught you really well how to talk to adults" or other things that acknowledge that there are skills involved, but the "what a natural angel descended into our lives!"
Similarly, I had a friend in high school who always commented on how "lucky" I was to get better grades than she did. Um, yeah, all that luck accumulated when I was sitting at my desk all night long....