Bay to Breakers

Born of California craziness, strange costumes eventually led to the craziest costume of all time, no clothes. Imagine running 7.5 miles with things flapping in the wind. Then getting to the finish line and waiting around. Very nice.

1960s College Campuses

The era of free-love was upon the nation/world. Chemical inspiration brought about mass streakings (is that even a word?). Naked hippies would eventually bring about the running revolution to follow in the 1970s. Once they cut their hair, got a job and put on weight.

Revolutionary War

The streaking and war gene was wiped out by angry Red Coats. War never mixed with streaking again.

Middle ages

Have a guy being running across a jousting arena, maybe being chased by a court jester or knight

Romans

Streaking was sometimes forced upon the people. Show a coliseum view with a naked slave/gladiator being chased by a lion.

Olympians

Sports and streaking was invented. Just that the athletes were naked, and the spectators clothed. Streakers would probably not be noticed.

Neanderthals

Streaking was hard in the ice ages. And no real point. Done on a dare when done. Maybe showing a cave man streaking in a cave with drawings on the wall and fire.