Aren't in-laws wonderful sometimes? God forbid you try to do something nice for THEIR child and ask them to help you out by babysitting THEIR grandchildren. The nerve of you! Sorry they're such a pain. I think in-laws need to come with a user's manual sometimes. 

I'm grumpy with my inlaws at the moment too. My birthday was two Saturdays ago, and DH asked them to babysit so he could take me out to dinner. MIL said no, as their kitchen is being renovated and she didn't want anybody over at their house. She didn't think she could come over to our house to babysit, either. So we arranged for DH's aunt and uncle to watch Em. When we went over to drop her off at the aunt and uncle's house, guess who was there? MIL and FIL! Apparently they'd decided to drop by Aunt and Uncle's house for dinner at the last minute, since they can't cook in their kitchen. So it's apparently fine to go out to dinner but not fine to come over and babysit their granddaughter...