Don't engage her.
When she starts, just yawn, say "whatever" and turn away to talk to someone else.
I wouldn't have a conversation with anyone who called me pathetic.

It really does sound like six of one, half a dozen of the other. She felt criticised when you didn't like the show she enjoys and you felt criticised when she didn't like the show you love.

If she's like this about everything, then I can imagine it gets wearing, but from this example it sounds like you both take it to heart if people don't like the same things you do.

You both sound really over invested for no particular reason that I can tell, and you both need to cool down. Can you just watch TV at your own house?

She didn't stop there and proceeded to dismantle a sitcom I absolutely love. Abit hyprocritical if you ask me.

Yes you are being a bit hypocritical. You told her why you didn't like her show. And shes done the same. It's fine.

It sounds like you’re 2 very different people. She sounds like she thinks that you think you’re better than her in some way, for instance in the fact that you don’t watch soaps and she does. I find that there’s a certain type of person who often thinks they’re ‘above’ watching soaps - I’ve come across several in my time.
The fact that you had to precede your qualifications with ‘I’m not being arrogant here’ IS being arrogant - your qualifications have nothing whatsoever to do with your AIBU, so why point it out?
Would you describe yourself as geeky? The fact that you could name all the cast of Hot Fuzz, which I doubt most others could, and that you go to conventions based on a sitcom are quite niche things.
At the end of the day, she’s your MIL. The mother of your spouse, grandmother to any children you have/may have. As my grandmother used to say, it wouldn’t do for us all to be the same, the world is a better place for all our differences.
Instead of getting mad at her, just enjoy the things you DO have in common.

Why do you persist in engaging with her, I'd be Hhaving the minimum of conversation. Why do you feel the need for a verbal essay on why you dont watch a light entertainment show, surely no is sufficient

I agree with this. You're both massively over invested about things you should be able to have a normal conversation about without getting offended.

People have different opinions and that's fine. If you can respect each other just don't discuss them.

You both watch too much TV! Seriously, this sort of thing is annoying. I do know people who are so invested in a show that they dislike criticism of it, or even indifference. It’s just best to not engage.

At a guess, does she feel threatened by you and not know what to talk about? Maybe TV is a subject she thinks you would be able to converse about as it's your area of study and work.
When you said that the TV show 'wasn't for you' did she hear 'I look down on it and people who watch it' ?
Sometimes it's easy to forget your privilege, if you have had the opportunity for education and career that she didn't that may affect how she feels about engaging with you. Out of courtesy you could be polite about the TV show and say you've never really watched.

It sounds like you try to be polite when giving your opinion while she is not and that is the important thing.

Interesting responses to this thread too, feels like people miss the nuance.

I wouldn't even go there.

I have an older relative who is similar with very strong opinions and I just avoid certain topics and keep conversation neutral. Or even avoid calling them when there's a big news story they'll have a lot to say on.

You're both in a power battle. Step out of it and kill it with kindness.

Saying you don't know who half the people are, on what i assume you think are low grade tv shows, does indeed have a subtext to it. Maybe live znd let live and offer to take her to a stand up gig. Try snd appreciate each others tastes more.

Where do you get that OP tried to be polite from? Those responses wouldn't come across to me as being polite at all. I wouldn't care, because I'm not over-invested in random shows like OP and her MIL are, but she knew MIL's views and continued to be rude. Being rude in the same pointless way about the same niche interests; the core issue is that they are too similar to other.

She’s touchy. You think you’re better than her. If you want to avoid this sort of argument in future, just watch out for when she’s getting touchy and stop talking at that point.

It sounds like you’re 2 very different people

I actually think it sounds like they're two very similar people.

OP I don't wish to be harsh but your post comes across just as opinionated and obsessive as you describe your MIL being.

You clearly have your opinions on the 'low-brow' TV and comedy that your MIL likes and it comes across loud and clear, as does your need to point out that your more niche shows and comedy are inherently better.

Going to a convention based around a sitcom would sit comfortably under the banner of 'obsessive'.

I wasn't at all surprised to read that you work in the media, your tone reminded me of several people I've encountered over the years. The very best of them was a BBC employee who told me 'I pay your wages'

You and your MIL sound like two magnets shoving each other the wrong way. Maybe you just need to avoid the whole topic of light entertainment and find things you can agree on.

YABU for writing this knowing no-one would think YABU.

You are as bad as each other, you just like different things. You do come across as an insufferable snob though.

Just shrug and respond with "Just as well we don't all like the same things isn't it? The world would be a pretty boring place if we did".

My adult daughter enjoys The Masked Singer (I guess that's the show) and when she told me about it I gave it a go but I didn't enjoy it, no big deal. She often jokes about us only watching Country File and Springwatch, which isn't the case but it's become a bit of a family joke.

You and your MIL do sound quite similar in that you both get het up about these things. Stop trying to justify your personal taste. Just say "horses for courses" and leave it at that.

It sounds like you try to be polite when giving your opinion while she is not and that is the important thing.

Interesting responses to this thread too, feels like people miss the nuance.

I would completely agree with this.

If my MIL called me ‘sad and pathetic’, there’d be no way I’d watch TV with her again, or have a lot to do with her! Did your spouse not say anything??
Just be polite to her if you ever have to see her and leave it at that. Don’t get into deep conversations about shit TV.

I don't see how pp can think that OP and her MIL are the same. I don't see where OP has flung out insults about her MIL's viewing habits or insulted her by calling her sad and pathetic - which is probably just MIL projecting her own insecurities onto OP!

OP, I would just stop engaging with her as soon as she starts getting nasty.

She sounds like a nightmare. You sound as if you think you're superior.

I was asked if I liked it your reply should have been "Not seen it" then either change the subject or walk away.
You must know what she's like, so stop feeding her reacting.

Who has the energy to care about this? My whole family come out with nonsense about telly, films etc. My best friend watches all the Married at First Sight stuff, I watch endless 'ambulance' shows.

Nod and smile, laugh about it. Invoking your degree subject is embarrassing.