AIBU to think my MIL is rattled by my opinion of her?

She clearly thinks your behaviour is unpleasant and I imagine if she posted a thread it would be a very different story.

Nobody knows what she has done (although of course plenty of people are on your side because it’s a MIL/SIL one) or whether either/both of you are being unreasonable.

Ultimately you married her son so you need to make the best of it.

I think people like the mil really believe that they’re nice people. Hence the shock and surprise when you see them.

it could be that she over egged the pudding once, you saw it and called it and she’s never been able to shake off that impression you have of her.
i think you do have the make of her most likely @AvocadoRules but her ego and need for public approval is all consuming

webhad neighbours like this, controlling, psychotic and irrational. They’d lie to us to try and get us to comply with their wishes- basically they didn’t want ANY vans coming up the driveway. The trees were protected (they were not) the pipes under the driveway were fragile ( nope) van drivers would come up and park on the driveway having their lunch… (erm no. Never happened). They’d tried to hit our vehicles with sticks and tried to block our driveway

4 years of litigation and we won.

all the while we loathed each other, but see them out on the roadway when they’re talking to other residents and they would wave and shout hello like we were old friends

I can only think that this was to spin a narrative that they’re polite to us and we’re rude to them.

the joke was that half the village knew what they were like and were right behind us “about time that pair met their match” and “good for you for giving them the bloody nose they deserve” the other half were team wanker and there’s no way they’d take us on.

Why do people believe this? If I didn’t like a relative and they stayed ‘cool and distant’ I would be delighted.

Given the OP hasn’t bothered giving examples then we don’t know how bad she apparently is.

If she is evil then she is not going to be ‘gutted’. If the OP just doesn’t like her then she will probably be relieved at an end to the OP behaving like she is.

People vastly overestimate the amount of head space that others give to them.

Stay cool and distant that will really wind her up!
She is clever enough to leave you alone, but will be gutted her nasty ways no longer bother you 😅

My good friend was in this position, in that she sussed the lie of the land pretty quickly, having entered the marriage full of good intentions, and over the years she refused to "rise to the bait". She bit her tongue a few times, but was unfailingly polite, if frequently "busy".
Eventually, MIL realised that my friend's DH, her own two DD's and SIL's were all politely keeping their distance where possible, so no gratifying upsets and dramas.
When she grew less active, and would have appreciated visits and support, she realised that all three siblings had opted to move away; although they would rally around in an emergency, it had to be organised rather than spontaneous.
I know there are many honourable exceptions to this rule, but family get-togethers tend to be the remit of the distaff side, and she had rubbed them all up the wrong way.

Has it occured to you that being treated by mil like this is hurtful? And hurt people do say hurtful things.
I have a neighbour just like OPs mil; she accuses me of being at the cause of everything so: apparently I kill ants the wrong way.Her fence was damaged in high winds but no, I must have kicked it in, my cat uses her garden as a toilet, she says, so she throws **it over fence. But our cat died in 2020 so,how? Apparently I am nasty because I don't talk to her every time she is putting out washing and she is going to tell the whole village how nasty I am. Apparently I wait till she is out then cut her hedge. I have footage of her looking over at ours,then cutting this herself. She tells everyone she is the lovliest person anyone could know and self promotes at every available opportunity.
She told neighbours other side that I was horrible to her,so they haven't spoken to me since. Never bothered to find out truth just,blanked us.
Narcicism is alive and well and can be found in all ages.

You give no examples of her behaviour. We just have to accept one side of the story. And asking us to suggest ways of having fun with her,winding her up,is totally unacceptable.

The way to deal with people you can't stand, be they a family member, 'friend' neighbor, or whoever.
Ignore them and get on with your own life.

I don't get why some need to get even or be proven to be the better person....it makes for an unhappy life imo.

I can’t imagine how or why there is any contact between you after both admitting you think the other is a horrible person. It’s odd.

Don’t let this awful person take up anymore of your time & energy than necessary

What a waste of your time and effort. If he was that bad a person he wouldn’t give a shit about your opinion.

I had FiL licked and he knew it. He was a functioning alcoholic surrounded by enablers. When DC was born he would make lots of passive aggressive comments about me returning to work or my weight, well, initially he did. My way of dealing with passive aggressive comments is to act like I didn’t hear them and ask them to repeat what they said. Then I say the question or comment back to them. They usually back down around then and I don’t need to actually respond.

He came from money, private schools, Oxbridge etc and I was the first generation to go to uni in my family. He liked to make lots of passive aggressive enquiries about the public education system. I think he was deeply insecure about the fact that I was clearly bright enough to see right through him and that my parents didn’t pay a penny for it.

I would watch him get drunk every night, making rude comments, being lairy with his wife, mean and combative with everyone else, before passing out. I never needed to say a word. He just knew that I saw him and he didn’t like it.

Nobody ever challenged him and said ‘Do you think you’ve had enough?’ Or ‘Maybe you should have a night off the booze tonight’ - I think he would have loved me to say either of these things so he had a solid reason to be disapproving of me. But I still never said a word to him about his drinking. Just quietly observed,

Ultimately his alcoholism killed him. Funeral was full of non ironic references to how much he ‘loved a drink’ and was such a great ‘drinking buddy’. It was really, really sad. Nobody could face what he was doing to himself, not even his spouse.

If you notice a truly unpleasant person just keep away. As soon as you start with the games trying to ‘out’ her you’re entirely on the same plane as her.

You could be better than that and not enjoy being awful to someone just because you can

Sorry Op but you come across as really nasty. You are asking us to suggest ways to annoy and upset your mil, just so you can have 'fun' ?? Grow up and learn to ignore her and be civil

You sound like a my daughter in law! Hope not lol

What has she done that is so horrible?

So you don’t like her and don’t want her speaking to you. You’ve manage to insult her so much, she’s been engaging less. Now you think you’ve manage to upset her even more, so want to try and wind her up to cause more upset

She may well be a narcissist but you’re the horrible person here. HTH

You're an adult. You don't have to have anything to do with your MIL. Drop the rope and let your husband maintain his relationship with his mother.

Do something better with your time.

Or.....I could have fun with this, but I don't know how.

We have very different ideas of fun 😐

I don't think there is the slightest danger of OP being changed. This is what she's like.

Which one is the narcissist again?

I love these posts where it all goes off the rails when the OP gets the opposite reaction from what they are expecting! Carry on.

What would Dolly do?

The misogyny and ageism on mumsnet is horrendous. Women trying to take other women down. The reason women have a small semblance of equality and equal opportunity is because women over 60 fought for it, on picket lines, in legal fights in courtroom, and with trade unions, and on marches. It cost some women their jobs but they were resilient. To hear women accusing other women of narcissistic behaviour because they don't agree with you, or have different standards of behaviour is awful. To deliberately set out to hurt another woman for any reason is just horrible.

100%

It's a power play. Younger women "decide" that older women are no longer needed (unless for childcare).