A little over six months ago I did it again: I said "yes", when what I actually should have said was "No thank you I don't want to do that".
One New Year's Eve I actually said "No thank you", and obviously it was way worse than if I'd just said "no", in the first place.
Having said "no", I left someone else in the difficult situation of having to find a replacement for me at short notice.
I think I also made it even worse by saying "There isn't a socially acceptable reason, I just don't want to do it" I suppose I could have come up with a reason, "I don't want to", sounds much more toddler than 45 year old responsible adult.
The important lesson I've taken from this experience is that saying "no" in the first place would have been a lot less stressful.
What do you wish you'd said no to?