AIBU to think my 3-year-old isn’t being “mean” and that family should stop taking it personally?

Really.
Giving kids a bit of time to think about things and calm down is now a frowned upon. Crikey.

Exactly and letting him get away with accusing someone of hitting him and not addressing those accusations could cause all sorts of problems going forward.

It’s a phase and with sensible measures will pass. I say sensible because accepting bad behaviour wont help but also dealing with it in a way that won’t make DS feel bad, just the behaviour. I think you got it OP.

Time out frowned upon now as well, world gone mad!

Because the world’s gone bloody mad, I used to nanny, this is what middle class kids are brought up like.

The 5 year old on the other thread shouted it wasn't his fault when his grandmother was repeating herself multiple times to him about it raining. It's not even close to the same thing as telling someone you don't like them and lying about his gran hitting him.

Why are you negotiating with a three year old. Pull him up, sharpish.

OP, is he only like this in his home/personal space? How is he getting on at nursery/play groups?

i know it’s hard pill to swallow when you seemingly good kid says this stuff and you don’t know where it is coming from.

saying how he feels isn’t wrong. Telling a lie is. He just needs help with the former (and that will come) and challenged on the latter in an appropriate way.

ps how did he get on with MIL before?

This.
His butt would be on time out. He doesnt get to rule the roost

There's another thread now about a five year old (debatably) being rude to his granny too. There's quite a lot of support for the kid because the granny was being indisputably very annoying, so where is the line? The granny on the other thread was equally unamused but because the adults also find what she did annoying it's OK? Presumably something this three year old's granny is doing is causing the similar reaction but he's unable to express why and apparently it's part of the end of society as we know it. Who decides what, when and where the line is that allows children to express their discomfort with something an adult is doing?

He's saying his grandmother hit him.

This isn't just he's telling her to go home. He's lying to the adults because at 3, he knows hitting is bad.

That's why OP's husband and his mom are upset. What were his consequences for lying? Well, his dad and grandmom are unhappy about his lying but they should just forget about that? He got to go to a party.

Although he is probably wanting things back to normal, you need to say that’s unkind and not let him be mean to MIL. If not checked he could go on saying mean things to get what he wants. It’s ok to say I know you are not happy at the minute but we don’t say unkind things and change the subject quickly keeping it upbeat.

He is 3 ... he doesn't understand how his actions effect others around him.
I'd talk to him and explain that it's unkind but the adults need to be adults for God's,sake and accept he is overwhelmed with mil there for a week he wants his normal back .

I honestly can't even begin with the mentality of some parents who would actually send a much loved grandparent home because a THREE YEAR OLD is acting out.

No wonder there are so many fractious family relationships on MN. And no wonder when I used teach undergrads in a university there were so many precious little petals who couldn't cope if the world wasn't ordered to their exact liking. They were probably ruling the roost at home from toddlerhood like this!

I’m gonna throw this out there. If ops fil died and she came to stay with op and her (frankly horrible) child and he was lying about her hitting him and shouting that she can’t sit down etc would pps still be saying ‘oh send the old biddy home!’ Or would that be unacceptable from the child?

Agree

He is experiencing jealousy i.e. not being the centre of attention - that needs to be dealt with as soon no-one will be able to visit for any period of time in your house

Or alternatively he'll do what just about every child of three does, which is to grow older and develop emotional maturity and this won't be a problem.

I'm not sure why it's OK to expect such sophisticated emotional regulation from a three year old when his father and grandmother don't seem to be managing it themselves very well!

In a round about way you have just told him that his behaviour is acceptable towards your MIL i.e. his Grandmother by giving him more time with you separately. He is experiencing jealousy i.e. not being the centre of attention - that needs to be dealt with as soon no-one will be able to visit for any period of time in your house. Having not long ago been told by a four year old to go home when visiting friends (his grandparents) it is extremely hurtful - your MIL must have felt so hurt. You need to step up and deal with his issues now before he becomes the one who controls you and everyone else. Your teaching him that he is the king of the castle when in fact you need to teach him that he is a part of a family not the front, centre and end of it. Assume this is your first child and therefore like all firsts he has always had full attention - that needs to stop - what happens when you have a second child if you decide to? Jealousy when allowed to bloom can be massively damaging and it is your job as a parent to manage it.

Our DD is very nearly 3 and she has these days - especially if something is out of routine or she is otherwise unsettled.
I think she is aware that she's being mean, but I don't think it is quite as intentional as an older child because at three, they don't really have the impulse control needed to make an informed decision. They get the urge to be mean, so they are mean. They can't logic their way out of that loop yet.
All the same, I don't tolerate her being unkind - I will pull her up on it and ask if she needs to go to her room to calm down (and follow through with taking her to her room to calm down if her behaviour persists), but I also try to make a note of what is bothering her and change the environment as reasonably if I can.
If people are visiting, we might hang out in her room just the two of us for stories and colouring, or if we're doing some DIY and things have moved about, I'll try to get her involved in some small way.
Also sometimes it's just that my attention has been divided and she needs it back, in which case when she's finished with her time out, I make an extra effort to play/bake/paint something fun that we both enjoy together.

Good luck OP - three is a challenge but you sound like a brilliant mum and I'm sure we'll both make it through in one piece 😂💞

Seriously, as someone whose family are very far away and therefore who had to have parents say for more than a month each time as otherwise we'd never see them/ it's just not worth it, we also needed space. I'd have taken my child out and love bombed them in that case. But at age three, I'd start trying to channelise feelings in a different way. 1:1 time with you will probably help.

Three year olds absolutely do have the ability to understand that they are saying unkind things and that pushing people is mean.

Of course, if he's overwhelmed and needs space while people are staying in his home, that's valid. But the parent/s should meet his need by taking him away somewhere else to have that space, not allowing him to meet that need by being unkind to another person or pushing them away and that going unchecked.

MIL also needs to understand it's not personal, he's not old enough yet to express what he really needs/feels and sometimes it comes out in this "meanness" because he is dysregulated and doesn't have the vocabulary to express it.

Yes, you can correct his behaviour, but it’s still ridiculous that they’re getting offended and taking it personally. They’re acting like children themselves.

Agree, and while absolutely she shouldn’t ‘go home’ because that’s what he wants, neither should she sit right next to him on the sofa because she wants if that’s what’s being referred to.

A three year old is not the boss. Grandparents shouldn’t be sent home because a three year old can’t behave. This is not on.