Aform of mass behavior that seemingly comes out of nowhere and disappears almost as quickly is called a

Fad

Explanation:

A fad is a type of collective behaviour that develops over a very short period of time. During this period, however, many people follow the behaviour in extreemly enthusiastic ways. Fads are usually sudden, quick-spreading and short-lived. Fads usually last only for the time period during which they are considered to be "cool."

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