When was the last time you immediately regretted something you said?

I have quite the selection, not of things I said that were negative or bad towards someone, but just things that contributed to my awkwardness, as this happens almost on a daily basis.

Most recently was when I was saying goodbye to a receptionist at a gym, she said see you on Monday, and instead of just saying something like "see you", because I knew I would see her on Monday, or anything else that made sense, I said, "why Monday?".