Mistakes were made . . .
Describe a time when you were just wrong on something and made yourself look stupid or ridiculous.
I'll start. In the process of editing an article with a professor and another person, I wrote that 'such and such should be put this certain way, because such and such is an adjective, describing that noun.'
It turns out that such and such wasn't actually an adjective.
I tried to interject some humor. Life goes on. But it's an ugly feeling.