I have a friend who has a lump in their belly button. I think I recall it being reddish brown, but apparently it does not hurt, does not ooze, or really do much at all, except get irritated if she plays with it but nothing extreme ("Like if a kid keeps pulling your ear lobes all day"). They admit their hygene wasn't always the best, though they don't remember ever being without it.
Is it anything to be concerned with? Could it just be some fungus? Would there be anything one could use to remove it?