"Dear Office Neighbor:
I know your 4 month old baby is super cute. And, I know that you can hardly stand to leave her at home. I know that you can't understand why I wouldn't want to hear her crying while I work on my spreadsheets. But, is it really necessary for you to bring her to work? Considering the fact that we don't work in a day care, school, maternity ward, social services agency, retail store, etc. I should think that my office would be the ONE PLACE in the world where babies don't make a regular occurance.
So, office neighbor, mind the infertiles among us and leave the baby at home.