Why do I always say stupid things?

It sounds like you beat yourself up a lot over every mistake you've ever made. Stop doing that and most of your problems will disappear. Everybody embaresses themselves sometimes and makes mistakes, i don't mean just once in a while, i mean, every day, over and over again, it's nothing to be ashamed of, it doesn't make you stupid, everybody does it. It's the only way to improve, to do things, make mistakes, listen to other peoples advice, and use the experience to do things better next time