A Kicker
A kicker is that one tiny thing that ruins your whole day. It’s like when you’re about to win, and your shoe falls off.
I was about to get a perfect score on the test. Then I realized I forgot to bring a pencil. That was a kicker.
My dog was about to win the dog show. Then he ate a whole bag of chips. That was a kicker.
I was about to get a promotion. Then I spilled coffee on my boss. That was a kicker.