AIBU to get pissed off with it and want to tell them to shut the fuck up.
There is a mum at DD2's school who cannot seem to say anything without a sting in the tail and a nasty dig. Our DDs are friends so it's difficult to keep a distance from her but I do try....
For example yesterday she approached me in the playground 'Hello, what have you been up to today?' Me 'Oh just a bit of housework, not much really'. Her (whilst throwing back head and laughing) 'Oh I'm really not one for housework. I prefer to actually spend time with my children rather than clean.
She is very competitive and seems intent on proving she is the best mother for some reason. 'Oh yes your DD goes to X dancing lessons doesn't she? My DD goes to Y for her lessons, they're more expensive there but then you get what you pay for with this kind of thing don't you?', and comments at 3 year old DS 'oooh what's mummy given you for a snack today then? Gosh, none of mine would know what that is as we're so health conscious'. She'll ask me a question and then use my reply as a springboard to make a put down and again try to prove to herself that she, of course, is better than me.
I feel like saying 'Yes, you win, you are the better mother/have the more advanced child' as soon as she opens her mouth!