I am SO rubbish at being assertive!!
....no, no, don't worry, I'll give up my day off tomorrow to look after your dc so you can go to your "really important meeting" that you've only just thought about getting cover for......
......no, no, I won't take my holiday that week, of course it'll be too difficult to get cover.......
......oh, don't worry that you haven't paid me, I don't have any bills to pay and the supermarket has a special offer on at the mo, all their food is free! and I love looking after your dc so much that I do it for free!!......
It's been one of those weeks (can you tell?) and it's only Tuesday!!!!!!! I wonder what I have to look forward to tomorrow?
Ooooh, I feel much better now!