Elementary, my dear boy!
It all started out when we all hunter-gatherers. While we were hunting and gathering, the richardest of them all said "Ooga ooga inga ah." In today's English, that translates to "All you guys suck because I'm the best." Everyone was concerned. Then, one of the arguing people said "Oo ooga inga." In today's English, this translates to "Your mother." Everyone was shocked, then the brother said "Ooga otaga ah." In today's English, this translates to "Aw snap." When that moment passed by, a new Insulting gene was created. From then on, the gene would never ever skip a generation. Ever.