I have the highest IQ in the world.
How do you know that you have the highest IQ?
Because I know that I am the most intelligent human in the world.
I know you feel like you're very intelligent, but it's rude to brag about it to others. It would be very difficult for you to know if you really are the smartest person in the world. Without definitive proof, you shouldn't claim that.
It's just a fact of life.
People don't like it when others brag. If you're smart, people will know if without you telling them, and they'll like you more for your modesty.