I'm not digging! the suggestion that he is 'cracking' when he just clearly cba with Rugby's ridiculous questions is a bit of a stretch.
The very fact that he's trying to imply that it's all beneath him is what shows he's cracking - because he just doesn't have any answers. A competent PM with nothing to hide would have no problem with answering tough questions.
The problem for him is that his normal response is along the lines of "This really isn't important, the public is much more interested in vaccination/Ukraine/ whatever else I can think of that isn't about parties or the economic shitshow". But, of course, the fact that this is all still in the news demonstrates that the public certainly is interested. More importantly, trying to imply that the huge constitutional implications around a PM lying to Parliament isn't important just shows that either he has no understanding of the constitution or he's backed into a corner and can't think of a way out.