There is a group with a website that is organizing La Tomatina-style tomato fights and providing mud pits for people to wallow in around the country. Here are pictures from an event they put on in Dallas this past November:
http://www.dallasobserver.com/slideshow/mud-fight-2011-35569827/ You can find the websites by putting in "dirty battle" for the mud or "tomato battle" for the tomatoes.
At their website they ask people to provide name, location and e mail and they say they will bring the event to a place where there is enough interest.
I would LOVE it if we could help these guys get a mud event put together on the East Coast this summer (Philly, Washington or New York). It would be a matter of deciding on a city where we could all meet. That mud looks awesome and I would love to play in it!
I love the idea that we are getting to the point where a group of 20 somethings decide that a fun afternoon out is going to an event where you get to play in the mud! Maybe we're in the "end times"?