I have been reading along here and feeling everybody's pain. I have a few to tell on my IL's ...soon to be ex mainly because my ex always believed that it must be all in my head.
MIL and SIL called me a rhymes with witch one Thanksgiving weekend because I had the audacity to ask my husband to help me please pack up the car. This was after she undermined my parenting when I told my 18 month old daughter to please stop playing with the dog so rough. Heaven forbid I didn't want my daughter to provoke the dog.

God Bless her but about 8 years later she waited until it was just us AND all of the kids in the car to go off on me being an ungrateful wench....that one my ex almost believed me because the kids were the first to tell him what she called me.
My exIl's always played favorites and my ex wasn't ever the favorite because he was the black sheep. My girls knew this and always wondered why those grandparents didn't love them like my mom and stepdad....you got it...my fault (according to ex...how? no clue but it is/was)
They promised my children that they would take all the kids to Disney World...guess who went and who didn't? Yup...all other grandkids AND their parents on their dime but we weren't even invited and then they were put out when I told my husband that he could go meet them at our airport for their layover that they called us about at 7 in the morning, the day of the layover but the girls and I had plans that could not be changed (band practice and something else). Again, somehow this became my fault.
I feel sorry for them...they missed out on 2 of the awsomest kids ever and my poor ex, even though he was right there, missed out on them too.
My daughter's are 19 and 15 now and whomever their partners in life end up being I hope that I always remember to do the opposite of these doofuses (or is the plural of doofus, doofi?)