I'm bad at no.
I was asked to do something recently which I would happily have done, but it was my birthday and so I said No. And I explained why.
The person pushed, and in the end I found myself agreeing to do it.
It was all OK, I had a pleasant enough evening, and my husband took me out to lunch instead, but the thing is, why couldn't I just stick to my guns and keep saying no?
It was perfectly reasonable, but I didn't say it. I am a push over it seems.