How to deal with the naysayers?

I have one brother-in-law who is such a pro at the passive aggressive remarks; it's driving me crazy during pregnancy. Today he asked me what formula I would be using, and when I responded that I wanted to nurse as long as possible, he said with a smirk, I give it two weeks! Last week he asked me if I was showing that much or if it was just my "frumpy" sweater. Just a few of many comments he's made since finding out I was expecting. Ugh, so over it and thinking of just calling him out directly once and for all. Any advice welcome!