Some years ago we had an acquaintance who took a sudden dislike to everything I did. No matter how trivial it was, she had a snide comment about it.
As a hostess gift we brought a nice bottle of wine to a gathering at her place. As is usual around here, the bottle was wrapped in a silver bag and trimmed with curling ribbon. This was a very bad thing.
During the party, I was having a conversation with another guest and our hostess was having a different conversation with someone else. They were right behind us and she pointedly said, 'Don't you think those silver bags from the liquor store are tacky?'
This was typical of the petty cracks she made every time we were together and I never knew why. She'd always been nice enough before but, for about six months, she was the epitome of nastiness.
I never said anything because, while the comments were made within my hearing, they were never made directly to me. Also, since each one was so minor, I was afraid I was over-reacting.
When an acquaintance seems to be continually offended, the only thing you can do is put on your Teflon jacket. It can be different with family but, at least with family, you can feel more free to confront the problem.