Do something low-inhib in public, eventually it will become easy. Once you have become comfortable doing something low-inhib, you can use that to rationalize any other low-inhib behaviors.
>For example, being loud in a quiet restaurant; well, if I can be loud in a quiet restaurant I can say something embarrassing in public; well, if I can say something embarrassing in public, I can also say something offensive in public; well, if I can say something offensive in public, I can also do something embarrassing in public; well, if I can do something embarrassing in public, I can also do something offensive in public; etc.
Be mindful of your impulses and instead of denying them, find a way to satiate them according to your situation.