To Tell SIL To Stop Claiming Things?

Just a firm no and an eye roll every single time.

When she asks I’d say ‘I’ll tell you what Katie, I’ll whip my dirty knickers off and you can have them as well’.

Really tricky. No one else has cracked it OP, so it's unlikely you will overnight.
The only thing I would do is talk to her 1:1 and say can I just let you know that there will be no food or other things to take home, please don't ask because refusal may cause offence. If that's likely to annoy, then do it before they come.
A personality trait that's a defence against something in hers or her parents past I would guess. Kind of compulsive.

How do you not rip the piss out of her every time she does it? If she tried this in my family she'd get roasted constantly!

You all sound very polite.

How do you know she’s ill ?

The more likely explanation is that she’s a CF of the first order and her behaviour is being reinforced constantly because she’s being allowed to carry on with it.

She sounds very difficult and stressful . It does sound like some sort of addictive behaviour pattern that she needs professional help with.
doesn’t help you right now - but I do think your DH should speak to his brother and say how it’s making you all feel and that she needs help.
Try to think - this isn’t you, she’s ill and hopefully it will be helped by next year.
dont enable it - pretend she’s a 6 year old asking for stuff, constant firm “Nos” and don’t give in or completely ignore. Don’t worry about how firm you have to be. Good luck!!!

Good of she gets embarrassed- it is an emotion humans have developed to stop them doing something socially inappropriate

I bet she laughs her arse off about it, no one who gets embarrassed behaves like that

I agree that folk like this have the hides of rhinos, @binkie163, but OP's BIL may well be embarrassed and putting it onto his DW as a cover ... in which case it would have been better if he'd declined the invitation for both of them to avoid unpleasantness

However he didn't so now it has to be dealt with, and any fallout will be for him to handle

I am sorry. Sending love from a fellow Coeliac.

PS mashed potato can be very soothing. x

Tell her to stop being so grabby. Tell her nothing is available for her to take home as you're dropping left overs off at a local shelter and keeping all your gifts for yourself. As you should.

Gosh your SIL is shameless OP! The absolute cheek of a GUEST telling OTHER GUESTS that they can’t eat as much Christmas dinner as they would like to because she wants to take it home for leftovers?! She’s actually limiting other peoples enjoyment of Xmas as she’s too tight to buy food! It’s not hers- it’s yours OP - she had no claim to your possessions or food.
I really hope you had the courage to speak to her - she does need to feel embarrassed about her behaviour. If she does end up coming round OP I would just tell your other guests to help themselves to as much as they like. May I ask OP (and I think I know the answer to this) but do BIL and SIL contribute anything to your xmas day (wine/ snacks etc) or at least bring you a host gift?

I don't think they like profanity on this site, so I will have to use a polite euphemism. I will quote what my Daddy used to tell us four children before we went anywhere:

#1 Don't ask me for (st!)
#2 Don't take (st) that ain't yours
#3 If you ain't buying it with your own money, its staying here!
#4 If we did want something he would ask "You got some XYZ money?!" If not he would default to #3 above.

So what you can do is channel my Daddy and tell her when she walks in the door "don't ask for s*t and you ain't taking s*t with you when you leave. If that's a problem, you can just leave now." And I would not care what anyone thought about it cause it's MY house and MY stuff and MY damn nerves!!

Your husband calls his brother and says : -

" We enjoy having family over for Christmas but if your wife behaves the way she did last year it will be the last time she's invited. Asking for other people's gifts and telling people not to eat too much so she can take leftovers home is not on. Please make sure it doesn't happen this year. "

You can't uninvite them now, that would be incredibly bad form.

bollocks to that. of course you can. Bad form is what SiL does. TBH bad form was OPs DH inviting them again without making it clear this behaviour is to stop.

I wouldn’t cancel this late but I would nip her comments in the bud the first time she does it this year.

She very manipulative, she has learnt when someone says something outright to stop scrounging to cry, so her H sticks up for her, so her behaviour goes unchecked. Everyone will be embarrassed and feel uncomfortable mixing with her @Addyview so if she can’t guarentee she won’t scrounge Christmas Day you have only one option to uninvite them.
When you arrange family meals out and they ask for an invite I’d be straight and tell them everyone is paying for their own meal so you naturally assumed they would refuse to pay so they weren’t invited.
Bullocks to pussy footing around them!

Why does it matter that it’s “bad form” to cancel ?

These people have demonstrated over and over again they have no time for the manners and niceties that oil the wheels of friendship.

Why should any courtesy be extended to them at all ?

People like this SIL only behave like they do because other people let them and don’t want to cause a scene or a fuss.

Fuck that. Tell them they’re no longer welcome. What’s the worst that can happen ? If they go NC well it’s no great loss and if they slate the OP and her family I suspect anyone who knows the situation will be silently applauding that FINALLY someone has had the balls to do something.

She is totally shameless. I'm cringing for you.
BIL is going along with it, so he is without shame as well
If it was just the food, you could say, no, that's there for everyone not just you but as she's like this with presents too, I'd Uninvite them both and have DH tell them why. Grabby bitch.
It's part of her personality now, so she won't stop and why should you be on edge waiting for her behaviour to appear?
Hell no

She doesn't get embarrassed she has more front than Harrods. I bet she laughs her arse off about it, no one who gets embarrassed behaves like that. She is like a dog pissing on everything to claim it.

DH are both in agreement that we need to say she can't behave like that because it makes everyone else awkward but BIL has asked us to leave it alone and just ignore her because she gets embarrassed.

So your DH has mentioned it to him in advance of them coming this Christmas and this was his response? Or is it something he's commented on in the past when you or DH have moaned about her?

*I'm half tempted to just cancel BIL and his wife altogether if I'm honest.
I'm several years into this womans impolite behaviour and it's casting a bit of a dark cloud over Christmas because I'm dreading her making everyone else feel uncomfortable when she starts! *

Well it's a bit late for that. You can't uninvite them now, that would be incredibly bad form. Also how the hell would you start to explain that? 'SIL we've been mulling it over and despite having a whole year to think about it, we've decided we don't like the way you behave at our house, so we are withdrawing the invitation of Christmas lunch at 2 days notice.'

So to me my two options are ring her in the morning and tell her to not behave that way or uninvite them both and tell BIL why. I simply cannot have another Christmas day like last years.

Option 1 is to shut her down the minute she starts, every single time. Be prepared for it and squash it the very second it starts, in the ways I described in my previous post.

Option 2 is get your DH to tell his brother in advance to tell her not to do it, because last year it pissed you off. If she still does it then revert to Option 1 and make a note not to invite them again. But you simply cannot uninvite them at this stage. That's very unreasonable.

Essentially, she's a thief. A greedy thief.

What's the deal OP? What's going to happen?

That guarantee might be invalid. I have a lifetime of family experience in this area. Its a psychological issue, and like any addiction, unsolvable by others.

Yes, your OH needs to get a grip and back you up. I have a sister with this kind of behaviour, not this petty and obvious though. It's a mental health issue enabled by her OH wanting a quiet life so ignoring it. Line in the sand today. Public calling out if she does it again. No future invitations. My local charity shop tells me it's astonishing how many people barter with them on the basis that the goods were free to them! (That's the ones that don't just walk out with them. They're not allowed to challenge and thieves know it )

You need to learn to be as brazen as she is. When she asks for something just say no.

Her: Can you save me some of that cheesecake to take home please?

You: No, we are planning on having it after supper tomorrow.

Her: Can I have that old air fryer now you've upgraded?

You: Well I was planning on selling it on marketplace for 30 quid, so if you'll give me 30 quid for it then fine. Otherwise I'm selling it.

Her: Please don't anyone eat the last of those sausage rolls, I want to take some home.

You: Tut SIL, what are you like?! (roll your eyes dramatically.) No your fine everyone, there here for you all to enjoy now. Eat as many as you like.

There is only one way to deal with cheeky, thick skinned people with no shame. Be as direct and blunt as they are.