Hissy is often used to describe a sound made by a cat or a snake, but it can also be used to describe a person who is easily angered, especially if they react with loud voices or angry words. Some synonyms for hissy might include irritable, testy, or snippy. These words describe someone who is quick to anger or annoyance, but may not necessarily exhibit the same kind of vocalization as a hiss. Other synonyms might include touchy, prickly, or edgy, which denote a general sense of irritability or tension. Whatever synonym you choose, try to use it in context to convey the specific mood or behavior you're trying to describe.