AIBU to be cross at my in-laws snub at my child’s 18th?

Sounds like you’re being a doormat, stop pandering to IL wishes. Why on earth are you spending £400 on SIL?? Absolutely ridiculous.

This is truly one for match energy. If they are playing games you just stay off the court.

Your children will feel what a real relationship is.

Encourage them to nurture real relationships and let others slide.

There are so many really nice, positive, warm, caring, fun individuals in the world that you can afford to let negative relationships slide.

Not everyone gets great family relationships. Clearly unfortunately that is what you were dealt with your DHs family.

They don’t care , so you don’t care either.

Drop the rope.

Take a huge step back and only see/communicate when you have to. Put them on a strict information diet.

You will be playing into their hands if you mention feeling upset about the birthday.
Remember, when they go low, we go high.

Act like they are so insignificant to you that you didn’t even notice the slight.

Precisely. I've reached that stage in my life where I simply don't care if people strop unreasonably. I only entertain reasonable grievances.

I wouldn't bother organising anything.

I would give your child the option of the money for the dinner, ask them would they prefer cash or a dinner with wider family.

Going forward you now know that things are no longer fussed about so you can completely drop the rope.

Maintaining the farce of a relationship with awful people is more damaging IMO.

Say nothing about it. Just move forward.

Match their energy. Who cares if they strop?

I'd ignore the snub.

They aren't going to get any mileage out of teen grandchildren who don't want to visit because they enjoy it. That ship has already sailed and there is nothing you can do to change it.

I'd also stop spending silly amounts on adult birthday presents.

If your dh wants to do something for his parents, fine, that is up to him but it's not your problem.

Did your SIL's milestone cost you £400 because she actually invited you to something, though?

Because your DC hasn’t really shown a lot of interest in spending time with them recently, and doesn’t communicate with them?

It's at least 50:50 fault here. You didn't invite them to anything, you didn't do anything, your son doesn't really get on with his grandparents anyway. They sent cards and money on the day. I can see why you wanted them to do more, but I think you set your expectations too high in the first place.

We didn’t celebrate PILs or SILs milestones on the day as they were doing other things. They usually go away on a big holiday to celebrate. It can be a month or 2 later till we get to it

They don’t sound in the least bit bothered about celebrating their birthdays with you and your family Op so bizarre to expect vice versa.

What have they done for your son’s 17 previous birthdays?

What’s the relationship normally like with those that gave nothing? What have they done for previous birthdays?

My DC had a milestone birthday recently. 4 sets of aunts/ uncles. 1 set gave a thoughtful gift, 1 a token amount of money and 2 absolutely nothing. By absolutely nothing, I mean 1 sent a text and the other didn't acknowledge at all, even when we saw them a couple of days later.

I was seriously annoyed but now I just think im going to match their energy in the future and not give them as much time and thought as I used to. Im the same as you, not bothered about myself but my kids definitely.

It sounds like you've imposed a different deadline for them to 'get to it' than you impose for yourself. Maybe they're just waiting for you to be available.

Your mistake was thinking because you arrange fun things for other people’s milestone birthdays they’ll offer the same in return.

Really you don't seem very keen or in any rush to let family join in a celebration. A date could be set any day.

I think your problem here is that you've over indulged your in-laws and pandered to their demands for their own milestone birthdays, when really you shouldn't have. They don't go out of way for you, so you should have pulled back years ago. This is a chance for you to reset - new standards have been set and now you can make minimal effort for birthdays. That's a good thing.

Re your DS - I expect adults to build relationships with children and if they are loving and attentive grandparents and aunties/uncles then I absolutely expect my dc to reply to grandparents texts and join a family group chat. If, at 18, they cba to make any effort with loving grandparents, then they don't deserve a big fuss and expensive presents. Obviously if those same adults didn't bother to build the relationships in the first place, then it's okay for kids to not go out of their way to see those adults later on.

But they didn't snub it, they sent cards and even some money.

You didn't invite them to celebrate with you and your son, so not entirely sure why you think that they would make a big fuss. When you explicitly didn't include them in your own big fuss

If you are saddled with people that accept hospitality but won’t offer it then your only option is to adapt your own behaviour.

Personally if someone has gone to the trouble of taking me out for my birthday, I like to reply in kind. The PIL obviously don’t think similarly.

What goes around comes around. If they're low effort with your DC at this pivotal age then they're going to be low priority for your DC when they're adults. It's the ILs loss, your DC will go on to form their own relationships and will have you and your DH.
My GPs were great, we had them for Christmas, I, and other cousin, cared for them towards the end of life. They were surrounded by family who loved them. Leave your ILs to their petty games now and leave them reap the consequences in the future.

What galvanised this thread two weeks later?

The skill here is not to react at all to the poor show from PIL and SiL. They want it to be noticed, they want a reaction. I would just carry on as planned, big smile when you next see/speak, don’t rise to it or you become the ‘bad one’.

This. Maybe it should be more unconditional from grandparents in the ideal world but maybe this can be a lesson for your now-adult child; if you don’t make even the slightest effort with people, they probably won’t bother too much back!