tips on radiance

My little monster co-worker used the T-slur today and I told him not to because its insensitive and he started arguing that its not (he's cis) and then later he called me the n word??????? And I told him to never say that again and that I was going to get him fired and he said "why do you take things so seriously, i was just joking!" and I told him that literally never matters and he was like "fine i just wont talk to you" and i was like good..... i cant believe this! i can't beleve how offended people get when you call them out for being racist/-ist in general instead of stopping to think like hey maybe my comments have ramifications im so mad.