At the top of the list of things not to say to your pregnant wife as she is putting on her pajamas:
"Heh. You look really funny right now," followed by uncontrolled laughter.
Next on the list of reactions not to have when your pregnant wife looks hurt and asks you why:
"Well your belly is huge and your pants are all pulled up over it [laughter] and you just look hilarious and adorable," followed by uncontrolled laughter.
And finally, on the list of reactions not to have when your pregnant wife loses her ever-diminishing patience and grabs her shirt, hikes it over her belly (revealing the entire giant lump in the process), and says heatedly, "Well, it's either up HERE [pulls pants further up over belly] or down HERE [pulls pants down under belly]. I don't exactly have a MIDDLE right now!":