I loathe the mysogynism of the HofC and the boys club atmosphere but in Cameron's defence, if you actually watched what happened, he used an unfortunate turn of phrase and it was everyone's reaction around him that caused him to behave in the way he did. I think he gave up so as not to prolong the innuendo.
Not saying it was right or pleasant but I don't think he deliberately set out to insult her in that way (she had worked on the amendment to the bill for six years and she was frustrated by what she deemed to be the Tories capitulating to the Lib Dems on the matter and he started off by trying to acknowledge exactly that).
He apparently rung her up afterwards to apologise. She in turn was quite sensible and gracious about the incident on Newsnight when I watched it for two mins just now.
I know that doesn't excuse everyone's reaction around him though but I don't think he was personally to blame.