You've read about them in the news. Parties where parents expose their children to the measles, believing this will give them some natural immunity to the disease. Most of these people believe that vaccines can be harmful, for example, that vaccines cause autism.
Regardless of whether you think these parties are good for your kids, or you side with the scientific medical experts who want to stab your children with needles, you can surely get the conversation started with your Measles Party t-shirt.
When someone asks, just say "yeah, I was there at one of the first measles parties, it was great, and yeah, we did wipe used tissues on our tongues, but hey, I didn't get the autism so I think it worked out great!".