I find it offensive to make fun an ethnical holiday. Those people don't have the opportunity to celebrate their national feasts in their own African countries, their homelands, and celebrate a feast for all Africans together, because they were mixed up by slavery.
BTW, an ethnical/national holiday celebrated with a meal is allowed by strict Hallacha. A religious holiday not stated in the Torah is forbidden to both Jews and Gentiles. But you do the opposite: respect Christmas which a new religious holiday (forbidden not only for being from a non-Torah religion, but especially because men must not create any religious holiday, even a Noahide is forbidden to create his own holidays!) but make fun of Kwanza!!!!!