Silliness in the heat of the moment
Hot weather occasionally makes people do crazy things.
In the summer of 1974, for example, it caused some people to become public exhibitionists. Strangely, their sanity wasn’t really questioned at the time, only their choice of outfits, especially when those choosing to run naked through crowds were hairy, out-of-shape men.
Streaking wasn’t done to cool off, only to look cool — or so the nudists thought. In retrospect, those appearances were definitely deceiving and the participants daffy.