Perhaps it didn't "start" with "off-color ribbing" but the usage of 'jokes' (see: Radio Télévision Libre des Mille Collines) to desensitize people to hatred towards the Tutsis is well documented.
It was unpopular to speak out against this sort of thing, and certainly was something that got worse over time.
Further, racial violence in the Americas didn't start with jokes either, it started with the genocide the Indigenous peoples of the Americas and continued with the trans-Atlantic slave trade ...