I think it is somehow related to Communism. It is my understanding that it started out in commemoration of the labor strike that got out of hand in Chicago in 1886.
Haymarket affair (also called Haymarket massacre)
So May Day events are historically associated with violence. That’s why the heads-up.
I agree, I was being a little sarcastic.
If The Communist May Day riots can extend to Cinco de Mayo, maybe the Latino Treyvon crowd can join in?