How do I ignore my MIL?

By far the most interesting discussion this week on the 'Married in Japan' (Yahoo! group) postings has been on the subject of the Japanese MIL (mother-in-law). Started by a young mum who is being driven potty by her live-in in-laws, her rant has generated dozens of posts, offering sympathy, commiseration and advice from deep in the trenches.
It seems Japanese MILs share certain characteristics, chief among them being an unwillingness to accept non-Japanese ways of caring for baby and an obsession with gaijin hygiene, or lack thereof. More than one DIL mentioned how she'd been instructed by her MIL not to wash her underwear with the family's laundry, or had been relegated to being the last person in the house to use the o-furo bath water each night.
The bath struck a chord with me. Not that I live with MIL or have been asked to reuse the bath water of someone else. But I remember the first time I went for a bath with my MIL at the onsen, it scandalized my mother and sisters back in England. How could I possibly have appeared naked in front of my MIL??? I had taken a giant step beyond the pail of civilized behaviour, from which they have yet to recover. Of course I insisted that in Japan it was common as anything to bath with your relatives and that no-one stared at anyone else's bodies, but they didn't believe that. It did take something to overcome my ingrained shyness and expose myself like that, but it was either bite on the bullet or forego the pleasure of the onsen and I figured the sooner I got used to it, the better. Ironically it was the first and only time my MIL suggested we use the onsen together. So maybe she felt as uncomfortable as I did, after all?
Even in households where DIL and MIL get along, it seems things can turn quickly sour after the arrival of a baby. MIL wants to wrap baby in layers and layers in spite of the heat, MIL wants to use kimono-style onesies, MIL is suspicious that those boobs can produce enough good milk for baby. One post counselled patience in the face of extreme provocation. The correct response to unwelcome advice, downright criticism or blatant wrong-headedness was a calm and collected 'Wakarimashita. I understand.' If only I could have taken that sensible advice on board!
As far as me and MIL go, the score is 1-1. I made her cry once, and she made he bawl once. I made her cry when I blew up at her for doing my washing (am I wrong to believe I should have the right to wash my own undies?). She made me cry when I came back from a weekend trip to find she'd cut chibbi-chan some very short bangs. My child looked like someone else. I erupted into a major tantrum, making chibbi-chan cry too, and refused to eat dinner or have anything to do with my in-laws or YK (who had been present at the time of the calamity) that night.
After that debacle, I decided I would show more restraint. I would accept that I was now part of MIL's family and that meant that homeland security on certain boundaries would occasionally be breached. Likewise, I don't think MIL will attempt another hairdressing adventure in the near future. These days she buys chibbi-chan mountains of hair grips and bands to keep her hair from poking in her eyes as the bangs grow out. I know it bothers them, but I'm Mum!