Thanks to this sort of thread previously, my response to my friend discovering she was expecting DS3 was 'three boys, lovely!' with the sort of enthusiasm I usually reserve for a nice cup of tea and some cake. As I have one DD myself, she almost certainly thought I was taking the piss. :o
With an only DC, and knowing what a lot of people think of that, I'm really wary of my reactions to people's family size. So it made me LOL when two mothers of three were all 'OMG, four!!!' to another mum at school.
I figure we're always wrong in our assumptions about family size and composition anyway. I nearly said to my neighbour (who has DS and DD) 'imagine if we didn't have girls, there wouldn't be farking beads all over the place' (dog was trying to eat them, they were bouncing everywhere, the girls were getting the strings for threading them all tangled ...) Ten minutes later the DS and his friend were making bracelets as well.