To me, it really depends on what you're aiming at. Like, for example, there's tribes that only center around specific people, like people that like icecream, so the name would probably have to do with icecream. Or it's purpose. If you want to make friends using that tribe, it can be named something like "Find A Friend Tribe". If it's just random, I would go with anything that sounds aesthetically pleasing. (Or derpy names. I like derpy names, too.)