There are so many tribes worldwide that are not well known. It's too expansive of a question to answer completely...but here are a few of the most interesting or bizarre:
1. Padaung - the tribe in Thailand of Burmese descent, where the women wear coiled rings around their necks, pushing their rib cages down. Interesting, because if the rings are removed, their necks would collapse. Some also wear them around their ankles and legs, wrists and forearms. They don't mind being photographed at all and there are trips you can take to see them. (and buy their crafts) The trips can be found in the northern Thai city of Chaing Mai.
2. Wahooli - of New Guinea. A tribe that first had contact with the outside world in 1973, and responded by moving deeper into the forest. They have no shame, no written language, wear no clothes at all, no leadership and almost no social structure whatsoever.
3. The Rondoks - of the Aru Sea in Indonesia. They have a "rat room" where the person who desires to be the Chief of the Tribe is required to live for a period of time in a shallow man hole, covered with a lid, with 30-40 rats. Most people who try to visit them disappear and Indonesia doesn't include them on their maps.
4. The Shans, in upper Burma - These are the Elephant People. Once every four years they steal elephant dung and bake it, then eat it. Nobody knows exactly why they do this, but it has something to do with their belief that the elephant represents fertility, prosperity, and unity.
5. Mongoni - This is a tribe that lives near Nyasaland. They think they are more beautiful if they cut big chunks of themselves off...like pieces of their butts, part of their arm, a chunk of a thigh, etc. The people walk around looking like grotesque creatures, but in their eyes...these are the loveliest people.
6. Plashwits - Turkistan. These are the Mouse People. They believe that to be strong and to be a man, one must be able to carry a live mouse in their mouth for miles without causing any harm to the mouse!
7. Quevalo - a tribe in Ecuador. They have an interesting tradition of a Feasting Ceremony every four years, when the donkeys are brought into the villages and bathed. Then the donkeys are brought into their huts, where they are indulged in rich foods and delicacies. The women stroke the donkey's penises and there is some donkey-woman sex that goes on, but nobody knows whether it's oral, anal, or vaginal...or what exactly...but it's done to the point of ejaculation. When the donkey vomits the rich food, the vomit is consumed gratefully by the family. Don't ask me why!!!!