Wow, lots of responses. It's been interesting. I can't respond to all but a few things:
The window thing is a specific issue - I don't know what they're called but we have those windows where they're either open a little from the top, or fully from the side. And when they're open fully from the side, they usually swing open all the way so that the window is completely uncovered. The particular window they used is the one that basically is next to the front door so about as visible as is possible to be. And as DH said when I spoke with him this morning (he's furious) he has repeatedly reminded DS that this window is a risk for all of us and he needs to be careful about keeping it properly closed (or open on the minor side). I did laugh at the people asking about not being allowed to open windows - we have many many windows in our house, all of which are regularly opened on the "top" way, but this specific window is never open at all at night, and definitely not open ALL the way.
@ToBeDetermined yes - I did specifically talk about a known gang of young teenagers causing problems in the neighbourhood. That was actually what got through to DS and why, I think, he was crying (in my bedroom, away from his friend) - he suddenly realised that these boys (who he has had run ins with in the past - one actually attacked him once) would 100% have come through our window and/or attacked him and his friend if they'd caught them or seen them. Ditto, a few weeks ago we had police in the neighbourbood as a group of boys (I assume the known gang, but I don't know) was going around destroying street signs in the middle of the night.
@BertieBotts useful, balanced advice in the context of ADHD as always. Thank you. There were a few others too, and I'm grateful to be reminded of the additional effort required with children with ADHD.
@MrRydersParlourGame The fact that DS did feel he could come to me upset and apologise means I think your comments are happening but I really like your mum's approach and I think I am going to be more explicit on that in the future.
I love all the refernces to "in a very scary way". I think actually, that was more in line with the teacher who can silence a crowd with a look - They knew I was being serious but I was absolutely furious but in control and I was "shouting" in that my voice was definitely raised. But as I said, I wasn't screaming and yelling.
@medik7 hahaha - right, I should easily have calmed down in just 10 minutes. I was on MN because my adrenaline was off the charts, I had sent them to bed and certainly didn't want to be down there berating them further. MN was a useful outlet to get opinions, express my frustration and NOT to give them a further bollocking while I calmed down.
Finally, I just want to say that actually, I agree that shouty parents are not great and that actually, a lot of the children with no boundaries etc come from the shouty households - I think it starts to roll off their backs and they just don't even notice it. One of the boys from the "gang" I referenced lives fairly close to us and I am afraid I have seen his mother and grandmother shouting at him on multiple occassions when he was younger. Clearly, as has been pointed out, that has not helped him at all. But there is a huge difference between being absolutely livid on one specific occasion when the boys behaved really really badly, and routinely shouting and screaming at them at all times and in all places.
THe friend is awake and DS is still asleep. I'm about to wake him up. I'll be reminding them both why this wasn't okay but there won't be any shouting at all. And the consequences are, not surprisingly I think, no sleepovers for a while. I won't be doing any further punishments. DS will be getting another bollocking from DH though who is even more annoyed about the window than me as he has had conversations with DS about that window and it's unique risks before.