I know what you mean. My DS1 has a friend he plays with a lot. I loathe this child's mother, she is so incredibly smug about her PP.
We were at a children's party, and one of the other mothers, who has 2 boys and then a girl, was saying how she really wanted a daughter when she was pregnant the third time, and had that child been a boy she would have probably gone on to try for a fourth time. Really honest if you ask me, and I knew just how she felt. Well my 'enemy' said that this was a horrible attitude, that she should be pleased with whatever she had etc etc..... very easy to say when you have one of each. Her final comment of 'Only the most shallow of people would care what they were having' made me snap and I will admit I told her to shut her mouth!