The definition of a bull in a china shop is:
(noun) a clumsy person, a careless person
The 5 year-old boy was like a bull in a china shop when he visited his grandmother. He caused a lot of damage by knocking over and breaking a lot of her expensive things.
After Shawn got drunk, he was acting like a bull in a china shop. We got kicked out of the pub because he broke all of our glasses!