SeeThruIt said:
I think it's rooted into my personality from being brought up around judgemental friends and family who loved to gossip.
This is absolutely normal. Worrying about what others think about you is as natural as eating or wanting to bang hot women. Those who say they don't care what others think of them are lying, either to themselves or others.
As others have said, catching yourself in the act is half the battle. The other half is forcing yourself to continue to behave AS IF nobody around you could hear you, or force your mind to remember that they really don't care one way or other.
This will take constant vigilance. The more you practice, the easier it will get.
Making it a habit of "acting out" in public will help you "get over this" quicker.
There's a guy named Hypnotica who is a supposed seduction guru, and he allegedly made a special hat with a big dildo on the front. Then he walked around town for a couple of weeks, and after nobody really did anything other than look at him funny, he realized deep in his gut that the opinion of others REALLY IS worthless.
Just do whatever it takes to build up as much "experience" of other people's opinions being worthless. This means doing stupid things and saying stupid things and noticing that nobody really cares.
There's a school of therapy called "Rational Emotive Behavior Therapy" that has people write out checks for two grapes at the grocery store, or go into McDonalds and order a pizza, or introduce themselves to strangers as "Mr. Peanut Butter" just to build up the "experience" of "other people's opinions don't mean crap."
The ABSOLUTE QUICKEST way (other than wearing a dildo on your head) would be to number close every single girl you see for the next two weeks.
Whatever you do, realize it will take practice. No simple mind trick or metaphor reframe will help.
Practice Practice Practice.