AIBU to not want them to drop in randomly to watch trains?

Well the person who says the OP is being unreasonable obviously thinks she should open her house to anyone who wants to watch trains...

OP if you look at the Real Time trains app it shows what's coming through, not just the trains that stop but also the ones that are passing through. And if you look at websites you can also see if eg the Flying Scotsman is coming through.
eg here: https://watercressline.co.uk/special-days/flying-scotsman-experiences/

If your friend encourages her son to join a local spotters group (he can sit on forums online) then he will likely meet people on the station that he 'knows' from the forums/spotters' groups. Far nicer to watch for trains with a group of likeminded people than a disinterested mum.

My opinion - you sound very kind and understanding towards your friend and her situation but I don’t believe that she doesn’t understand the impact on you. You have told her it stresses you out and it’s difficult for you. She just does not care about the impact it has on you.

How the fuck is it goady? 🤔

Yes it’s diesels DS loves most. I have had the pleasure of going to diesel galas with him which to me just seem to be very smelly!

but it keeps him happy!

@FlatPat rather than explaining to her how it feels for you (again), just tell her not to do it.

Explaining to people can be helpful sometimes, but it can also make the ‘no’ quieter. Some people have to hear the ‘no’ very loudly before they listen.

So, ‘sorry Jenny, don’t come over unexpectedly .’

She said she has told friend she needs advance notice, she is autistic and it stresses her out. The friend has ignored her.

Can you please explain why you think OP is being unreasonable?

Next time they come tell them you’re just going out, they can go round to station.
Theyll have much more fun with fellow spotters anyway, & won’t notice you haven’t gone out?

Yes, just do this.

To me it comes across as someone looking for ideas how to handle a situation delicately

I don’t think it does at all.

OP - Yanbu. Send her a message now saying you can’t do it any longer. I’d avoid saying without warning as someone this intent on pleasing her son at your expense may just start dropping in weekly
warnings, and continuing to come as much.

So when she buzzes and you realise it’s her, you say “sorry, it’s not convenient, you will have to let me know and make proper arrangements next time.”

It doesn’t come across like that to me at all.

No it doesn’t at all come across as an attempt for a pile on

You are not being unreasonable. It is incredibly rude of her to ignore your request regarding unannounced visits to your home. Keep it simple, tell her one last time, very firmly, and if she persists then stop answering the door.

Why?? You mean you'd be happy for people to frequently just arrive unannounced to sit in your house to watch the trains? I certainly wouldn't like it. If they asked in advance, leaving me the option to say sorry, no, if it wasn’t convenient for me, it would be different.

OP, YANBU at all. Just ask your friend to ask in advance in future (with a limit on no more than x times a month) as unannounced visits from anyone stress you out.

Edited to add: I see you say she has ignored your requests to ask you first. In that case you’ll have to get tougher. If it happens again, you could say "I’ve asked you before, I need some notice if you want to visit me to watch the trains. I don’t want to disappoint X so you can come in just this once, but it’s not to happen again. It’s not fair."

What an unreasonable response. We can have friends and call them that and still not want them dropping in unannounced.
If you read the thread Op has already said that she has asked the friend not to turn up unannounced.
OP may know how much the trains means to the autistic son of the friend but you could equally say the friend should know better than to drop in unannounced especially as she’s been asked not to. Why does the friends sons feelings matter more than OPs in her own home?!
It sounds like Op has been accommodating on several occasions.
Why would op tell them to piss off and never darken her door, she’s said she just wants notice. So it’s not all or nothing as you’re saying it is.

This thread comes across as goady and an attempt to get people to pile onto your 'friend'

Yabu

As a fellow autistic person, I can see how this would be a cause of stress and not a straight forward interaction. People turning up unexpected is a nightmare to me. If you feel you can address it in person, I’d centre the conversation around either an unplanned visit (so next time they just pop in) or if she mentions the trains. Eg “it would be lovely to see you (pleasantries ease any negative social inferences), but I can’t do now/then. If he does want to come over to watch trains please may you text me a few days in advance so I can check my schedule?” A text in advance would give you an opportunity to decline or prepare for guests.

Alternatively, if over text you can send a message like “hi, it’s so nice your little boy enjoys watching trains at my house. Would it be possible to plan these visits in advance, so I can make sure I’m free and he won’t be disappointed if you can’t come over?” That’s a very reasonable stance

Would you like to join them at the station for some trainspotting? So if they turn up at your door don't invite them in just grab your coat. Your friend is being rude, ignoring your limits, so don't worry that you are being rude if you're more forceful. It's great that you feel sympathy for her difficult situation but you don't have to put up with unwanted visits.

I’d hate this too- organised visits, great. Unexpected drop ins, absolutely not.
The best thing to do obviously is tell them this. But if you find it tricky, can you not just pretend to be out? Or would it be obvious you’re home/would they look through the window?
Ive definitely done the coat trick before when my in laws come round and my partner is out, see them pull up outside, grab my coat and head out then feign surprise when I see them there, and tell them I’m off to an appointment and running late!

Also, trains follow a schedule. There's absolutely no reason to show up unannounced.

I hate people turning up unaccounted too OP. This always causes controversy on MN where they say 'my front door is always open, as a kid we were in and out of everyone's homes, I love a random drop in- blah blah. Sounds like she is using your home as a drop in creche- even though she is staying there with the son. Its rude OP and YANBU.

Its not the 1960's with no mobiles, no phones or way to text and check its ok BEFOREHAND.

OP- If confronting them on the front door when they arrive is too difficult (I'd find this difficult and I'm not ND). Send a text now along the lines:
'Hi Jane, I'd appreciate you call/text before dropping in unannounced to my house. Its not always convenient (and you don't realise how much stress this causes me). Hope to see you are school/club/X soon,
All the best, FlatPat x'

Add the bracket section if want.

OP I don’t know anything about steam trains or special trains, but you could decide how often you feel comfortable with your friend and her son coming round. Then sit with her and look at a steam train timetable and schedule her visits in advance.

That way, you’re in charge of the frequency of the visits, and she can plan to take her son to the station instead on the other days.