@ArseMenagerie have you even read the OP's ousts?
Clearly not or you wouldn't be asking!
her DS hasn't had a poo in 10 days, tgats serious.
he was starting to poo & she knew her DH would lift him off the toilet.
she locked to door to prevent this and so DS would poo. In hindsight this wasn't her best idea ever, but when we're exhsusted & frustrated, we don't always make ghe best decisions.
her DH acted like a fucking idiot & scared DS (& her). There was no need, his wife was in there with their child, no one was in danger.
@Burstdoor yep, probably not your finest moment, but I get the exhaustion, frustration & worry. There was no need for DH to act like such a twat, none at all.
Does he understand how ill not pooing could make DS, or does he just think it's not a big deal?
it's good you're going to follow up on other things that might be causing it.
I'm sure you've heard all of this before, but...
Does DS have suppositories ? It needs to be 'softened' from both ends, not just orally. I see you write he won't poo in a nappy, but have you tried or asked him if he'd prefer to go in his pants or in the garden or a potty. Sometimes they're scared of losing it down the toilet. Another thing that can work is getting them to crouch, rather than sit. It's a much more natural position to poo.
it's very very frustrating when you'd got to a pretty good place, only to be set back by illness, but you will get there again.
I'd apologise for locking DH out, explain why you did it & see what he says. I'd expect a complete apology for his ridiculous behaviour & for him to say how he's going to deal with the door, & a promise not to do anything like it again, it was pure aggression to show his physical superiority.