"Wow, can't believe you just had a baby - you're so thin, you look fantastic."
This after I had just discussed with an acquaintence that DS was born 3 months premature and was in the NICU, and I had been hospitalized with complications from C-Section (which resulted in follow-on abdominal surgery and was unable to eat for 10 days).
This is no joke, but I will say, the stress of worrying about your severely premature baby is a great way to lose weight, if that kind of thing interests you...