I think the worst new year's resolution that I ever made was before I retired. I resolved not to work over the amount of hours that I was contracted to, (as I never finished on time - there was always so much to do). And I broke it when I went back to work on 2 January and got home late, yet again!
I didn't make any more new year resolutions after that, but if I resolve to do something differently, at any time of the year, I treat it similarly and usually stick to it.