What's Your Worst Quality?

So I haven't gotten this interview question since applying to be a camp counselor in high school, but have long since been practicing an answer to this question anyway. How do you answer "What's your worst quality?" in a way that doesn't totally suck? My answer from high school was a total basic bitch answer of "I am a people person and try to make everyone around me happy, even if that means I'm not happy." Not only does that not really apply to my personality, but it's also like the number one bad answer to that question.

Should I ever be put on the spot for this question, I'm wondering if my inability to get my "who" vs. "that" problem under control is applicable? Is being able to readily name one of my biggest grammatical flaws a strong enough answer to this question? Because in my mind, this just means I am in tune with myself, but also shows that I have great grammar skills to know that it's an issue.

I could even elaborate about how I would CTRL + F my work everyday to double check for any "that" "who" issues. I had a post-it note on my computer to remind myself to do it. And now I can almost always get it right on the first try after being called out on it so often, and learning to mercilessly scour my work for it. So there is even a success story at the end of this proposed answer.

I'm starting to this is the only really good answer possible to the "What's your worst quality?" question because it points out a clear flaw (but not a land mine of an answer), but also highlights what I do to combat my problem, which seems to me like a recipe for a good answer.

Recognition of a minor flaw + how you will/have fixed it = success.