Background - DD2 is 4 and a half. She has a full name, which we often call her by, and a nickname which is derived from that name, which we also often call her by. Say her name is Clarabelle (it's not) and we call her Clara as a nickname.
MIL and FIL, since she was born, call her by her nickname, but when referring to her full name, very often get it wrong. They'll say, for example 'Clarissa'. They do not do it maliciously, that's absolutely for sure. They see dd2 almost every day as we are neighbours. I always politely correct them. It's not happened for a while and I have been quietly referring to her by her full name in front of them, to get it into their heads.
However, today, DD2 was in a performance in our town, and afterwards, FIL introduced her to a friend of his, very proudly, as his 'granddaughter, Clarissa'. I firmly, but not angrily, said 'no, Clarabelle' and he said 'oh, it doesn't matter'. I strongly disagreed with him and said 'it does matter, it's her name, and it's been 4 and a half years now'. I said this very firmly although not aggressively. The poor woman who was being introduced looked horrified, and my MIL, who is lovely, rapidly changed the subject and tried to jolly us all along, which was probably good.
I chatted to him again after a minute in my normal way, I'm not normally so stern and I felt bad, but didn't bring it up again. Do I owe him an apology do you think? I asked dh and he just laughed weakly and would not be drawn. I am not scary, honest!
WIBU, considering he was trying to introduce us to someone and I made a bit of a scene?