To never invite them again.

I don't think they are holding anything over them they just didn't expect their holiday to be ruined by constant moaning which is fair enough. If the GF was unhappy with the facilities (that she hadn't paid for ) she should have kept it to herself and got on with things. And whether the grandparents paid for the holiday or not there was no excuse for the grandson to shout in his elderly grandmother's face. That is never acceptable

It’s interesting that her own DPs haven’t taken her away since she was a teen.

I know it’s like mumsnet bingo, but I do wonder if the DGF is neuro diverse, so out of sorts as out of her routine and her complaints were more her expressing confusion that aspects of the holiday were not how she expected them to be.

In any case I would speak to your DS asap about it. He needs to apologise to his DGPs. I would suggest he takes them out for a meal ( leave the GF at home).

Tell your DS he has to apologise to your parents, explain that he and his GF ruined everyone's holiday and that is not OK, they are old enough to know what they were doing and were being extremely childish and rude. If they stay together it will be a disaster.

You've made sure that you've acted in such a way that you've pushed them closer together, they're the only allies that they've got. Well done.

Wrong.

Expecting adult people to be pleasant traveling companions in gratitude for a gift of a holiday is not “holding it over them.”

I can't stand people who give something to others or pay for something and then hold it over them. Your parents need to give their heads a wobble and everyone else should stop feeling beholden to them. They paid, their choice.

That's a bit over-dramatic. OP's son's behaviour was pretty terrible but I've read about much worse behaviour on here, normally relating to domestic violence and sexual assault/rape committed by the OP's partner or husband.

Yes, I agree.

Behind the parents' anger is hurt.

Behind the son's anger is embarrassment.

Behind the girlfriend's behaviour is resentment (and/or boredom/entitlement/immaturity*)

And the OP is being used as the poor sod in the middle.

*take your pick

He sounds almost as bad! What entitlement and rudeness, plus ingratitude.

Please make it clear to him that behind your parents anger is hurt. They were looking forward to a nice holiday as a family which was ruined.
It’s a shame he’s in a relationship with somehow who he can’t grow with.

Shameful behaviour, which in time, he will become more aware of.

Good job on reprimanding them both. They both need a bit of a reality check.

I would tell DS that his girlfriend is not welcome back in your home until you get confirmation from GPs that both DS and his girlfriend go to GPs house and apologise to them in person for their behaviour.

I would then suggest to DS that the decent thing to do, would be to also save and book a short break away for his GPs to further apologise for ruining their holiday.

Honestly I think you need to make a real point out of not accepting this. He's obviously very fortunate and he's now crossed the line and perhaps a bit of that good fortune being removed would be a much needed reality check.

Does he pay anything to live at home? Does he do any domestic duties?

So he isn't even mature enough to own it and apologise and be ashamed of himself for his behaviour. Just scuttled off and hid and continues to hide.

Goodness, that’s all very OTT. Take a breath, go for a walk.

Jesus H Christ on a bike at Christmas…. This is quite possibly the most shocking behaviour I’ve ever read/heard. I would cry with happiness if somebody offered me to go on holiday with them, never mind offer to pay (I don’t have any friends or family) and would insist on paying for myself. If they wouldn’t accept payment then I’d make sure I paid for every meal out and that they were reimbursed that way. I’d do whatever they wanted when they wanted and not even dream of moaning! I’d also do all the cleaning & tidying, make every cup of tea and would thank them so much they’d be sick of hearing it… Because that’s how I was raised. I’m staggered. Truly staggered.

What?

Just roll over and accept rudeness because he 'likes her'

No!

Funny thing. I’ve got a cousin who didn’t have a lot growing up, nor did we really, but her parents split and she went with her mum and her abusive dad wangled it so he was way better off. No CSA etc. So she never went a family holiday, didn’t even leave the UK til she was an adult, didn’t get things every teen girl would want. It was clearly hard for her and uncles and aunts did their best to make up the shortfall.

She has a tendency to find fault in everything. The hotel room is too small/hot, she can only travel on certain forms of transport, she’ll ruin meals out, always has to huff /send hers back. Which would be fine but she can’t cook and isn’t arsed, so at home the food she makes is not the most amazing. I think she hides her insecurity in threatening situations by complaining, and the need for some sort of perceived status -and control - also come from her upbringing. What’s noticeable is, it’s always when someone else is paying. It’s like she feels being grateful (or at least politely pretending to be) is beneath her.

She’s way older than DS GF and has never grown out of it. Her DH has quite a life. I think it’d be a mistake to humour her. I’d tell DS frankly that she’s rude and you’re worried it’s contagious. I know conventional wisdom is don’t try to get between them but she’s done her best to wreck a holiday, so the genie’s sort of already out.

Yes. As I said in my original comment, I'm not excusing the behaviour.

Has he apologised to his grandparents? If not, why not?

I would tell my son that they both needed to thank the grandparents for paying fir their holiday. You ca t just accept their bad manners, you must call them out on it.

I'd not invite them again.

But the op says they could have got a taxi into town for less than a fiver.

It’s really weird, immature behaviour. Like something you’d expect from Kevin and Perry aged teens railing against parents curtailing their fun. Except these are 21/23 year olds, with full freedom. Why the hell didn’t they just go into the main resort after 11pm? Why didn’t she want him to swim in the pool?

Has there been any hints of poor behaviour from either of them before? I’d have personally sent them home.

I would let him cool down and reflect on his behaviour for a few days. He then needs to apologise to his grandparents and offer to reimburse the money for his and girlfriends stay. If you have some money perhaps you can treat your parents to a short break to make up for it?

I would back up grandad changing his will, he is clearly too immature to receive a lump of money. Would probably all disappear into taking the girlfriend on holidays that meet her exacting standards.

Clearly you won’t be taking the pair of them anywhere again but I’d be careful about excluding her from your house. You risk him siding with her and a major falling out. I suspect this relationship will come to an end soon.

The shouting at his grandmother who has been really poorly is unforgiveable. I really don't understand why he refuses to apologise. Surely, he must know that it was a terrible thing to do? He has suffered absolutely no consequences for his actions (as you have confirmed that your father's declaration of removing him from his will is an empty threat and he doesn't mean it).

You need to have a serious conversation with him. If he doesn't recognise how awful his girlfriend's behaviour was and how hurtful his verbal attack on his grandmother was, you have a massive problem.