I was at my inlaws house and bil and sil were mentioning that their friend was having her third baby. Step Fil's (as it's DH's step dad) only comment on the matter was "you think that by now they would have learnt to use contraception". He definitely wasn't joking given the tone of his voice. No one said anything about it or called him up on it. I should have at the time but didn't have the courage, and no doubt others would have jumped to his aid and defended him.
I know it's just a throw away commeny but AIBU to think it's a nasty and non of his business how many children other people have. Step Fil has no children of his own. He in general isn't that keen on people having children and can be vocal about it. He wasn't happy for us when me and dh were having a baby.