Bulls aren't "angry" all the time. They just get protective of their harem of cows during breeding time, and like to challenge the leader of their herd (which would be the farmer or rancher or another top bull) all the time to test their strength and bravery to keep at the top of the pecking order.
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It's not so much this particular motion and it's not so much that all bulls get angry at this movement. It's the particular type of bull bred for sporting/fighting purposes that "get angry" at this motion because they've been bred to do so because they feel it is a threat and it needs to be "dealt with" for lack of better terms.