The lip readers are almost entirely unanimous in agreeing he said stupid woman. That's what it looked like. It isn't the worst thing he could have muttered to himself but, as Labour leader insisting he's not a misogynist, he wants a gentler kind of politics without personal insults, he'd have been better advised to fess up. Yes, I mumbled to myself, no I wouldn't have said it publicly, I'm sorry if I offended anyone but - Mrs May leads this government, the worst government, here's a list of all the terrible things etc etc etc.
One of JC's difficulties is what seems to be an inability to face criticism or challenges. He goes into grumpy old man mode (whoops did I say that out loud)