What is the worst thing you have ever accidentally said to someone?

I don’t mean things like “I hope you die” (in my opinion, that’s not an accident). It could be to a stranger, or to someone you care abut. For example, when I broke up with my college boyfriend of three years, he said, “I was going to propose to you.” I responded (without thinking about it), “Oh God, no.” Obviously, this was not the most delicate way to put the answer, but I was so upset that things had fallen apart so badly that we were in completely different places. I’ve always felt guilty about those three words, and I’m sure I’m not the only one who’s made a blunder like that. So what did you say, to whom, and have you ever been able to apologize and make it right?