A Juggalo (male or female) or Juggalette (more commonly used for a female) is a member of the group that has grown up around the fanbase of the Michigan rap/horrorcore group Insane Clown Posse (ICP), and related recording artists at Psychopathic Records.
Generally Juggalos/lettes lack hygiene, literacy, respect, and employment. They can be identified by their distinct odor, and annoying chants.
Basically, if you see one at a Tech N9ne concert, stand far away from them. I went to a Tech N9ne concert in I think November, and it was like 10 degrees out, there were juggalos in shorts and wife beaters on, and some of them were pouring faygo all over themselves, and spraying it all over everyone in line. Fucking gay.