Finding "zany" activities in San Francisco should be pretty easy!

A few thoughts...
Drag shows/clubs in the Castro
Body-surfing in our cold & shark-infested waters (bay or ocean)
Something crazy down Lombard street?
Lombard Street (San Francisco - Wikipedia, the free encyclopedia)
Alcatraz prison tours -
Alcatraz Island (U.S. National Park Service)
The Pacifica "Fog Fest", which is from Sept. 29-30... Pacifica is supposedly the foggiest city in the US, which they celebrate every fall.
See Beach Blanket Babylon, a San Francisco tradition -
Steve Silver's - Beach Blanket Babylon
Pumpkin-patch touring in Half Moon Bay -
Half Moon Bay Pumpkin Patches
That's all I can think of now, but I'll post more if I come up with anything... in the meantime, try the SFGate website for events info.