To think he should consider things before now?

[Noonelikesasloppytrifle]

I am going out for the entire day with my eldest DS tomorrow. It has long been planned and is for a special occasion. This means DH is in charge of school pickup and activities tomorrow evening for other dc. There are a few added complications in that one DC needs collecting earlier and the other one can't miss the activity as it is their last ever session. All of this was known well in advance.

DH is now flapping tonight trying to figure out the logistics of tomorrow around his work schedule. As all of these were known entities, with plenty of warning, I'm not sure why it has come to the night before and he's only just realised what needs to happen. His ability to think ahead is notoriously poor, it just doesn't occur to him. I'm not sure he'd have remembered any of the above unless I'd prompted with the information. My sympathy and tolerance levels for his conundrum are low. He thinks I'm a miserable cow. AIBU?

Whereas I hear your frustration, I am inclined to think that, as you know His ability to think ahead is notoriously poor, it just doesn't occur to him, then I would have reminders in place.
In the same way that my dh helps me with things I find more challenging, before people jump on and talk about wife work.
My dsis almost certainly has ADHD. We are all aware of that, and do what we can to make things that involve remembering dates / understanding "if she needs to be a X by 3.30pm she will have to have left Y by 2.45" easier for her, because it is something she really struggles with.
OTOH, she is really artistic and has beautiful handwriting, so she helps me out when I need something like that doing.

To me, if a person struggles with executive function, then you do what you can to support them through it.

My DP is exactly the same and I understand that he struggles but it is so exhausting to do anything different due to all the reminders I have to put in place at the right time. I do think he should take more responsibly though and definitely not be grumpy about it. I don't think you are unreasonable at all but sadly I have no solution. Hope you have an amazing day out

He doesn’t think ahead for these things because he doesn’t see it as a priority. Like men and buying presents, it’s not genetic, they just can’t be arsed.
He’s an adult so presumably capable of figuring out the logistics if he’s motivated to do so. You’re not being a cow, he’s just being unreasonable and hoping to somehow dodge the burden of responsibility