1. Never ask a woman if she's pregnant or assume she is unless you are 100 percent sure.
The reasoning behind this: believe me, you don't want to guess wrong.
2. Never, EVER touch a pregnant woman's belly without asking permission unless you know her pretty damn well. I have no problem with close friends and family rubbing the Buddha but everyone's boundaries are different. Hell, I've had complete strangers touch my stomach and it was only through a supreme act of self control that I didn't completely flip out on them even though I know they meant well.
The reasoning behind this: personal space is personal space and everyone is entitled to it.
3. NEVER, EVER, EVER ask a pregnant woman if she's expecting twins, no matter how big she may appear to you unless you are seeking an alternative to suicide by cop. This happened to me today and I'm not even that bloody big. I'm big, but not crazy big. At the very least, I deserve to be canonized for not ripping this eejit's stupid smile right off his face. Here's the Pope's mailing address for you to send your letters of support: His Holiness Pope Benedict XVI 00120 Vatican City, Italy, Europe.
The reasoning behind this: is obvious.