When you ridicule someone, you mock or make fun of them. They become the object of your ridicule or mockery. Your bad behavior might bring ridicule on your parents, who raised you to know better.
The word ridicule is related to ridiculous. If you ridicule a friend, you try to make them look ridiculous. But now that isn't very friendly! Both words come from the Latin redire which means to laugh. When you are ridiculed, you are made a laughing stock, but being the object of ridicule is never funny.