The Bay to Breakers Race happens once every summer in San Francisco. It's a running race that starts in the city and ends somewhere on the other side of the peninsula on the Pacific coast. There are a small number of serious runners who take part, but for the most part it's just tens of thousands of drunken college students.
The tradition is for people to show up to the race dressed up in a crazy costume and armed with lots of beer and liquor. Here are some pictures of the debauchery as it passed by my house. If I had known it was going to be such fun I would have taken part!
There were tens of thousands of drunk people. It was less of a race and more of a spontaneous parade.

This year there was an effort to crack down on the drinking and prevent people from bringing huge floats. Eventually, the crackdown was abandoned though. Here are some people protesting the crackdown on fun.

The floats were hilarious. There isn't any way to have motor-powered floats, so they're all human-powered. This float had about a dozen ropes attached to the front, which were being pulled by some runners.

There was some construction going on at a building adjacent to the race route. Here are some drunken people dancing to loud music on the scaffolding.

Here's some naked old dudes.