I once worked in a modern school during a time-period when blue and purple nail polish were very in style in certain circles, and all the girls were wearing blue and purple nail polish.
I really wanted to wear blue nail polish, so I decided to wear it on Purim, since I figured it’s the one day a year I could get away with it. However, when I was about to wash for the Seudah on Purim night, I suddenly realized that I had to take it off if I wanted to wash. I figured that it was a bigger Mitzvah to have a seudah Purim night than to wear blue nailpolish – so there went the blue nailpolish! Oh, well. Boruch Hashem, I got a Mitzvah instead.