It was that last sketch, with a senile Sherlock Holmes that did for me. I don't know whether it was my recent plunge into Sherlock and it's fandom, or just that the whole idea of any person, but particularly one that brilliant, losing it all, and still being aware of what it is that's gone... I was in floods.
And then there was the last 'Remain Indoors' sketch when David takes Rob's hand at the end. I was sniffing a bit at that too. But I did manage to laugh long and hard in the middle with the 'Sorry' sketch though. God, all of the ones when they're just being them are the funniest ones imo. I laughed so hard at 'we can't keep on being alternative' and 'Peep Show won't last forever, you know'. I hated 'Sorry' back in the day - the thought that David might remake it - the horror, the horror! :)