things like "Jo, you're pregnant!" (had absolutely no idea why it looked like I'd eaten a football...)
Also, "whose is it?"... When I had a Fiancee. (Actually I haven't told anyone, it's been a secret till now, but it was a totally immaculate conception...)
It get's worse when your baby arrives too. I regularly get asked how old my boy is... "He's 17 months old..." and I keep getting this answer... "NO! Are you sure? He looks much older and bigger than that!"... YES, I AM sure... I do KNOW when I had him, that kind of pain isn't something you forget that fast!
I think for me the most horrendous one was being asked just weeks before I was due to give birth, in the middle of a shop by an old lady, extremely loudly... "Why didn't you use contraception?"