The hypothetical bull who somehow materializes in a china shop isn't trying to wreak havoc and destroy the proprietor's livelihood. He doesn't mean to knock over shelves and smash plates and teacups left and right. But he does anyway, and if he gets agitated at all the noise and mess he's causing, things will certainly get worse before they get better.
I somehow doubt a live, healthy bull has ever really shown up in such a place. But the scene is easy to visualize, and provides one of the more colorful idioms in the English language. In common usage, a "bull in a china shop" is someone who, lacking any ill intent, nevertheless ruins something important with his awkwardness, clumsiness, or lack of precision or tact. He could be the lethargic museum custodian who knocks over antique vases while dusting them, or perhaps the ill-informed diplomat who unknowingly offends his hosts and leads his country into war.
The socially inept boor is quite often totally unaware of his incomptence, ignoring the obvious even when others begin to shun him. Hooray for him, I guess, but woe to those who have to deal with him. His physically clumsy counterpart can't help but notice the chaos and destruction that follow him, unwilling priest of Nyarlathotep.
Physical bulk and strength combined with inadequate fine motor control and general airheadedness can lead to some seriously embarrassing situations. The human bull, even when he manages to avoid his porcelain-lined nemesis, still breaks stuff and makes messes at a far greater rate than his nimble peers. He walks into people carrying hot coffee. He drops dumbbells on his toes. His handwriting is illegible, and his typed efforts boast several errors per paragraph, even after years of practice. He nearly burns down the chemistry lab. Twice.
He gives his own team's quarterback a concussion during practice. He falls over the feet of the girl who tries to teach him to dance. She finally gives up after two weeks; he can't meet her eyes for the rest of the year.
Halfway through college, he realizes he might develop into a pretty good mathematician. | 
