While a three-year-old child's irrational overreaction to a situation might be considered a temper tantrum, a similar response from an adult could earn the proper description "hissy fit." This is somewhat similar to a conniption fit or a tantrum, but is generally applied to someone who has already demonstrated diva-like or high-strung behavior. A nervous bride might have a hissy fit after being told the caterer has abandoned his post, for instance. While the situation may still be under control, the bride may have a temporary emotional outburst triggered by a combination of stress, pressure and nerves. The term is almost exclusively ascribed to women, although some men have been known to have similar over-the-top reactions to distressing news.
The origin of the term is a bit of a mystery, although there are a few working theories. Some believe it was inspired by the sudden and ferocious hissing sounds a cat produces when cornered or confronted by a rival. The hissing might be accompanied by a convincing, if largely ineffectual, display of bared teeth and claws. A person having a hissy fit might also affect such a provocative pose and display flashes of anger. There's little historical evidence to back up this theory, but the comparison between a cornered animal and a person having a tantrum is often accurate.
Another theory is that the "hissy" is derived from the word "hysterical," which originally applied to irrational behavior displayed by women. Certainly a person in the throws of a hissy fit does display overly emotional or hysterical behavior, so the connection between the words does sound plausible. The term is considered to be regional, however, so if it is indeed slang for a hysterical outburst, it did not become universally popular.
There is also the possibility that a hissy fit is derived from the same root as "histrionics," which describes dramatic behavior considered inappropriate for the circumstances. People who suffer from histrionic personality disorder, for example, may display the same lack of emotional control as someone having this type of fit. It's possible that the term became shorthand for a histrionic outburst, although it's not clear whether or not a complex term such as "histrionics" would have made it into the popular vernacular.