For the last two years, my PILs have been very respectful about their smoking when we (I and my two DCs) are at their house.
When we are there, they and my DH have only smoked in the garage which adjoins their kitchen and we in the lounge can't even smell it.
But the last time we went which was a couple of months ago, my MIL stood in the hall and smoked, so she was literally only feet away from my DCs, blowing smoke into the lounge.
When we went home I asked my D if he wouldn't mind asking her not to do that and all I got was "it's her house, she can smoke in it if she likes" and he refused. At a later date, he brought it up again after an argument and told me he wasn't going to invite me and my DCs to his parents' house again because of this.
This hurt me a lot as I really like my PILs and want to have a good relationship with them.
Yesterday was my DD's 3rd birthday and his parents came. The very first thing his mother said was a "Oh, you haven't changed then," which was a slight dig about that fact it has been so long since we saw them, he might have changed his appearance in that time.
I waited till his mum was alone and basically very politely put the possibility to her of not smoking while we were there. She was a little defensive at first and I got a bit of a lecture but she was OK and said that she would respect my request as she liked me - we had a hug and I cried a bit as it was an uncomfortable conversation and I dislike conflict.
Then she said she would have a word with DH.
Now he is being really cool with me. He hasn't spoken to me about it but I can tell he isn't happy that I spoke to his mum about it.