There are really only a handful of last names in Mali, and many of them can trace their heritage back to the great Malian empires that most of us just glazed over in our history classes (Ghana, Mali, Songhai, etc).
Through some long and complicated historical process (that also isn't really written down), a national joke has developed in Mali whereby every family name is joking cousins with another.
As a Kone, I mostly joke with Traores, but also joke with the Coulibalys and a few others. When they meet you, people usually inquire about your last name to ascertain if they are your joking cousin. If they are, then you are free to say terrible things about each others' family - such as "Traores are donkeys"; "Traores are toads"; or "Traores eat beans" (because beans make you fart, and let's face it - farting is universally funny). Other variations on the theme include the less-creative but still totally acceptable, "Traore bad, Kone good," and the historically-insensitive, but somehow still funny, "Traores are my slaves" (I'm not yet culturally integrated enough to be comfortable with that one).
This is a ubiquitous part of the culture. I probably find new joking cousins at the rate of a couple a day, and maybe a dozen when I go to market. I have two joking cousins at the mayor's office, and we say bad things about each others' families when we greet every morning. It's especially nice for me, because it allows for instant ice-breakers, and people are additionally amused that the white boy is in on the whole thing.
It amuses me that this joke is the same every time, and is still just as funny. It's kinda like mom jokes, or "that's what she said" jokes. Ironically enough, the only thing off-limits within joking cousins is peoples' moms... go figure.
I can only imagine that this all arose out of a troubled past, in which these relationships were somewhat-less joking. From here, it seems like a brilliant way to bridge ethnicities, brush over historical rivalries, and prevent conflict. One can't help but wonder if this system might have helped my dear European ancestors.