Because you can't say anything back. If we would complain to our friends they would suggest their personal trainers or diets.
You are simply there for venting purposes just repeat, "You're beautiful baby, what are you talking about?" and you will be just fine.
EDITED: I hope you knew the backlash you would get when asking this question. I personally don't really care you asked this question but I am very relaxed now, but not every woman is. And yes it IS painful and awful and well you get it. Also count your blessings for not having to endure child birth. Thats all I have to say. :]