Whether it's somehow useful or not, it sounds like you've realized that attitude is doing more harm than good. That's a good thing.
Start telling yourself a different story. If someone says you're being silly and you start to think "They must mean I'm dumb," tell yourself that's not true (you're not dumb, and that's not what they meant anyway). Tell yourself that-- and this is important-- whether or not you believe it. You've already got the first part of this; you recognize that you have the bad habit of letting those self-destructive thoughts win out. Next time you think one, contradict it. "They probably mean I should let this topic go or not worry about it. Maybe they're just not comfortable discussing this." At first, you may keep believing the negative thoughts anyway, but once you get into the habit of telling those thoughts off, you'll be able to choose what you want to believe. Choose to give yourself the benefit of the doubt.
Another part of this is simply to concern yourself less with what others think (or especially what you only think they think). They don't know you as well as you do, they never will, and even if they could, they're only other humans. Sometimes they'll have something useful and good to contribute, but if they really are mocking you it's to hide their own insecurities and ignorance. No matter what, they can only do damage if you believe the things they say. So don't. Be polite, be kind, but believe in your own perspective. You know better.
