An annual event that I first witnessed at Carnegie Mellon University. Sponsored by cmuOUT, the idea is to wear jeans on one specific day to show your support for alternative lifestyles. According to a web page I found about the subject (http://www.cs.cmu.edu/~dtw/GJD/), this has been around since 1973 or earlier.
While I believe in equality as much as the next guy, the obvious flaw in this event's design is that a lot of people wear jeans without regard to their views on sexuality. The College Republicans club on campus in 1996 tried to bring this out in the open by encouraging its members to wear khakis instead on that day.
I forget what day this was in the past academic year, but I wear jeans pretty much every day. So I can safely say that I'm making a difference in the world today.