My head is spinning. Am I in the wrong here or is he?!

When I disagree with mine, he says I’m shouting at him

I have done the old, that’s not shouting, THIS IS SHOUTING ( honestly I was so tired of being accused of shouting, so I did )

Still insists I am shouting though, when I disagree with him.

Fine. Don't 'threaten' him then.

Just say 'The holiday is booked for x date to x date.'

Then it's up to you whether you remind him about it at all. He can just be a no show in the event that he's kicked off about it or something else in the meantime - you'll still get the holiday.

Although, tbh, I'd be sorely tempted to bypass the 'if' and go straight to 'I'm tired of all this 'oh, the scary lady's threatening me' bollocks. I want a divorce. Nope, no if about it, no 'threat', I'm done' as nobody should have to live in an environment when two letters kicks off an immediate 'YOU'RE THREATENING ME'.

It's still an "if .. then" statement though.

I can't imagine approaching my DH with a statement like that tbh (too convoluted). I would simply say, "we need to get xyz sorted, what are we doing about it?" and progress to resolution from there.

But I don't think the problem here is really in sentence construction, is it.

Sure does

I would suggest that he views the potential consequences of his lack of action as a threat from you, because you can and should be preventing those negative things happening by doing everything yourself, to his mind. He sounds like a child and totally insufferable.

Why does everybody have to have a condition ???
Could it possibly be just that’s his an idiot, & he’s deflecting from his disorganisation with bullshit of he finds “ if “ & “I’m cancelling “ threatening!
Like WTAF !

He needs a diaper change

This sounds pretty hard to manage. If this is the only problem and you just want ideas to solve it, then one approach might be (and this is really treating him like a child) to phrase it as two options so he feels more like he's making an informed joint decision rather than responding to a deadline. So, "here are our options, we get this booked now and keep the original dates, or we take more time and change the dates to the next set work will approve".

ah sorry I misread your post.
i imagine though, that op just saying ‘if’ isn’t the only thing he complains about. He sounds like a very selfish, manipulative, passive aggressive, gaslighting, childish twat. I’d definitely be rethinking my relationship with him. I agree with the just doing it method rather than consulting her DH or trying to get him to commit to something but it makes me wonder if maybe just saying ‘if’ to him isn’t the only thing he shuts op down about. He sounds unbearable.

As in, she books it and he either doesn't come as he hasn't booked the time off, or she books dates that suit her and he is the one left stressing about it, because he didn't tell her by the deadline she clearly communicated.

I mean, I agree, if course she shouldn't have to stop saying "if". But following through and letting him suffer the consequence, rather than trying to remind him multiple times (which she shouldn't be having to do anyway) just takes away his argument completely, so there's nothing to gaslight about.
He will try and spin it onto her whatever happens so she may as well save herself an argument plus a load of back and forth stress, and go straight to the consequence.

Why should op stop saying if? Her choice of language isn’t wrong. OP’s gaslighting OH twisting it back on her for his own fuckupery is the issue here. Even if op stopped saying the word if, he would use it against her no matter how she phrased things. Why should op pussyfoot about for her snowflake DH when he’s the one in the wrong! He’s just trying to shut op down for the stress he’s causing her and basically telling her to shut up and put up with his shit behaviour because he feels ‘threatened’.

He’s treating a boundary from you at his faffing around as a threat. I think that is worrying and very bad for you. You sound as though you’re being reasonable.
I once had an indecisive partner who was indecisive (because he evidently wanted someone else and left me) who used to accuse me of being as I was at work (teacher) because I explained my boundaries. Infuriating!

Is he autistic with pathological demand avoidance? If there are techniques you can learn to support him.

Just stop saying "if", and do the thing you're needing to say "if" about. So for example, DH hasn't given you dates for holiday. Don't tell him that if he doesn't soon, you'll go without him / pick dates that suit you and he'll have to work around it Just DO that.
Actions speak louder than words - he'll soon get organised.
When he asks why you didn't tell him, just say you're avoiding the "if" sentences like he asked.
He sounds irritatingly disorganised though.

Really, so you would be dragging your feet and f**ing up the plans and if anyone tells of you natural consequences of that you “would not be responding well”??

are you having a laugh?

Book for yourself and DS and go without him. He can catch up if he wants to. Sounds like you'll have a better time without him.

Agree with this - childish, manipulative, gaslighting, selfish, self centred, passive aggressive behaviour.
I’ve come across some passive aggressive, manipulative behaviour from people in my life but I’ve never heard anything like the op’s situation. It’s quite frankly pathetic behaviour from him.

Yup! Manipulative much. Designed to make op shut up and put up.

He’s being passive aggressive, and instead of accepting the blame for his fuck up, he’s turning it back on you so he can be the victim.

He sounds emotionally abusive and gaslighting you into feeling like you’re threatening him. It’s not a threat. At the end of the day him purposely dragging his heels in situations so much that it causes you a lot of stress then tries to twist it back on you to make you feel like you are the problem and that you are ‘threatening him’ is gaslighting. The fact that he doesn’t seem to care that it’s giving you stress and would rather claim you are threatening by trying to get HIM to make a decision he doesn’t seem to want to make himself shows what sort of an absolute twat he is. What do you actually see in this man and what benefit are you getting out of the relationship by staying with him?

Personally I could not stay with some snowflake who thinks saying the word ‘if’ is threatening. Tell him to grow up and get a grip!

‘if we can’t organise the holiday asap then i will need to move the dates for work and we’ll have to cancel these suggested dates.’*

Just rephrase what you want to say.

” have to confirm work holiday dates by xx. Should I change them?”

NU to use ‘if’, in itself. But, now you know he finds it triggering, unnecessarily confrontational to continue using it.

I was going to suggest saying any news on the annual leave front etc.

Think it would be best to ask him how he wants to be asked? What he would do the other way round? He's setting you up all the time. This would so wind me up. He's totally unreasonable and on the boundary of gaslighting.

Why do you book your time off before agreeing dates with him? Sounds unnecessarily stressful and results in your making what he considers threats. Or why don't you just make the plans and let him know what they are if he has trouble committing and you have put your stake in the ground at work? Have you decided yet where to go/what to do, or is that a whole other debate?

I suspect he doesn't really care whether you have to change your (perhaps prematurely arranged) annual leave, yet doesn't want an earful about it before and after you have to do it, or be reminded ('nagged') about his failure to confirm.

When married I sometimes got into situations a bit like this, and looking back I think towards the end part of me perversely wanted to be able to blame him for things so I think there was a sense in which we played to one another's weaknesses. I've been divorced for a while now and absolutely relish not ever having to negotiate this kind of thing, which can raise hackles on both sides.