Ohh that sucks so much, I had someone tell me he didn't want to see my "creepy alien photos" when we showed the first 3D scans we got - it was our gender announcement because the pic had "It's a boy!" written on it.
Your MIL putting that on Facebook is despicable! But completely more embarrassing for her, because now everyone you know knows how much of a cruel person she is so to say something like that about her own grandchild.
Your bubba is gorgeous btw!! Great 3D pic it's so hard to get a good image when they're so little and this one is awesome!