I think it's impossible to convey on here the subtle family dynamics which make us react the way we do to seemingly inocuous behaviour. My MIL for example has regarded me as lower than an amoeba since I met dh eleven years ago. Before we were married she was very vocal about it, sent us abusive letters, refused to have me in her house, called me horrible names to other family members. Since the wedding and especially the children, she has been much more cooperative and really quite supportive of us at times, and I appreciate it, although we will never be close. I try very hard not to bear grudges and I am pleased that she behaves more civilly now. However she makes virtually no effort to see the children - she has only been here two or three times since ds1 was born (she has a car, is very wealthy and travels all over the world on her own - I think she's in Prague this week). We go to her house with the children for a family get-together every February, and are treated like second-class citizens because her elder son and his girlfriend are rich, successful and work in the City. I don't care about any of that crap and I do try not to let it interfere with her and the children enjoying the short time they have together.
However, given the background to our reltaionship, I do take exception to some of the things she does which I feel are disrespectful of me as their mother. When ds1 was 2 and we had travelled for 6 hours to get to her house, I called her from the train and said that ds1 would not need to eat when we arrived, he was exhausted and would need to go straight to bed (it was 11pm). She agreed. When we arrived she literally snatched him out of my arms and took him into her kitchen, where she proceeded to feed him a yoghurt, nagging him about spilling it down his front (he still remembers that because he thought it was odd that she should mind him getting food on his bib!). When she arrived to see ds2 (he was about a week old), not having seen any of us for almost a year, she strode into the room, snatched the baby out of my arms and took him into the kitchen. She hadn't even said "hello". I also remember little things like her swinging ds2 in his baby bouncer after I had asked her not to - she didn't mean him any harm but it really made me nervous. Also her pretending that we were all going on a "nice family walk" when ds1 was 2 and ds2 was only 3mo - it turned out to be an 8-mile trek to dh's father's grave . She gave me no opportunity to prepare ds1 for this, she just went her own way.
So I can see 22ann's point, if it's part of a build-up of disrespectful and undermining behaviour. I do bite my tongue with MIL because she's not a bad old stick really, she really does love dh and the boys in her own very limited way, she is just a pain in the arse. But I think if I had to see her more frequently and have an ongoing day-to-day relationship, then I would have to put my foot down about some things for my own sanity.
Another old auntie, by contrast, stuffs them full of chocs/crap, takes them out into the garden, sneaks in to watch them sleeping - and it diesn't rub me up the wrong way, somehow, because I know she isn't making a point, and she doesn't want to take over, she just loves children!