There's huge amounts of history there, so I sort of know the reasons why this happens (nothing I've done, other than be myself - I think that MIL is just seething with jealousy about me, and she has been weird about FIL showing me any favour in the past too). BIL's ex-wife was put on a pedestal because she was plain and unremarkable in every way and not very bright, thus not a threat to MIL - she could control her, whereas she has no chance of controlling me. I can see why it happens, but it's still upsetting. My husband has brought it up a few times, and then they suddenly play dumb and throw out excuses like they didn't see it, they don't know how facebook algorithms work, or they got distracted just before they were going to like it. Whatever.