My SiL is a serious CF.
When her kids were young and we didn't have ours, she'd ring me up, out of the blue and tell me I had to be at hers in 20 minutes, to take her and the kids out.
I'd explain that I was out and about, it'd be at least an hour and to call my wife to get ready. I'd get home, my wife was still in bed and we'd get over there. SiL would wait by the window until she saw the car, then phone and scream abuse at me.
At the door, she'd shout more, " How dare you! I told you to be here at 10! Why did you even bother? You've ruined my day!" She'd then feed the kids, even if it wasn't lunchtime, before insisting that we go where she'd wanted.
She didn't drive and also never had the car seats. I got to asking her and she'd scream at me, saying that it wasn't necessary for them - at 1 &4! I used to call her husband and pick them up, as it was directly en route.
I asked why she was so horrible and asked my wife to stick up for me, she said that I'd provoked her and anyway, I swore at her and called her nasty names. That was completely untrue, as I was on eggshells round her and would take a book to another room, rather than be in the same space.
One day, she called and ordered me to be her chauffeur. I explained that, sorry, I was busy going to see the bank manager and that she needed to give a day of notice. She screamed and swore and then hung up.
A few minutes later, my wife came downstairs and said that she'd had her sister on the phone, weeping hysterically and listing all of my screaming and swearing and how I'd called her a cunt, a bitch and a whore.
She told SiL that she was lying, as she'd heard everything. SiL hung up and wouldn't talk to her for a month.
My wife admitted that she'd never heard me shout or swear at her, she had been taking her sister's word for it. The penny dropped for me.
I try to have as little as possible to do with her. She also never ever once thanked me for taking her and her kids out, paying for their food, or offered petrol money.