My best guess is that if people are telling you, in a critical way, that you say ‘stupid things,’ they probably mean that you have a tendency to speak before you think, and that you are sometimes rude, or maybe just a little annoying, as a result. That is a good behavior to correct! I am sure you don’t mean to do it. Maybe these people could be a little more polite in how they express their criticism, but honestly, there are more important things than politeness. So long as they are not being unfair or abusive, I think it is pretty much always better to focus on your own behavior than on the behavior of others, when they are trying to tell you that you have done something wrong.