You will need to clearly define for yourself what exactly is "stupid things" to say. Consider what you may call stupid might in fact be a good joke or add a bit of humour to a situation. So you really walk a fine line between what you can call stupid and parody. Like you said they can be part of your personality. Now one is perfect and we all say something that we wish we'd have phrased somewhat differently later. The question is how often have other people actually noticed?
Perhaps the focus should be on what you would rather do or be. Perhaps things like: eloqant in your speech, able to speak clearly on a variety of subjects, able to tell a joke in the appropriate settings. Or just plain developing the knack of saying the right thing at the right time.
Look in the direction you want to go.
Alex
