I'll give a brief summary of MIL.... 
Wrecked wedding (paid for whole of DH's Clampitts family) to go to Las Vegas for our wedding) as refused to speak on day, sat sour faced next to me at Spago's in Caesar's Palace and moaned about everything, never said congratulations to either of us.
DH booked a weekend away for when DD3 was 6 weeks old and MIL promised to come and stay with me to help. She didn't turn up, rang 2 hours before he was going and said she was "depressed" but we found out that she went to a christening of a friend's granddaughter instead. DH went away and I was left alone with 2 under 16 months and a 6 year old. Fair enough but DH wouldn't have booked it had his mother not agreed to stay.
Never reliable. Asked 2 years ago for her to look after DD3 (6 months old at the time) while I (DH was away working) took 10 children including DD2 (aged 2) to DD1's Build a Bear party. She didn't turn up and left me high and dry because she was upset I didn't want her to come to the party(!)
Last one that has caused DH to stop speaking to her was that she sided with her daughter who owes us £5000. DH asked his sister nicely if there was any chance of us getting the money back, his mother decided then not to ring us, ignored us when we rang her and the following week arranged a memorial for his other sister, for the first birthday since she passed away last year and didn't invite him. This last incident has hurt DH massively and funnily, she thinks we've fell out with her over the money (which isn't anything to do with her) and has no idea how her actions affect her children.
What hurt me hugely is one day when we were having lunch with her at her house, DD1 asked with bright eyes if she could sleep over there and MIL replied "NO CHANCE, I don't have any of the grandkids staying, can't start it with you cos they will want to stay". Motherfucking bitch.
So to summarise MIL - she is selfish to the core. She prioritises herself, never does anything for our DDs and always lets us down. Funny thing is that she has all the time in the world, she doesn't work and is single.
She is jealous to be honest. Jealous that her son loves me more than her. Which isn't fucking hard to be fair!
There is loads more but that's a whole other thread....