Are my friends joking around or being racist and how can i make them stop?

Some of my friends have suddenly started to make comments that make me uncomfortableand I dont know what to do!. they refer to native americans as 'bogs' and imitate thier accent. Also they refer to chinese ppl as cinos and also imitate thier accent. They refer to east indian ppl as SN's. the S stands for sand, and the N stands for the N word. They seem like they are just joking - they are good ppl and are not actually racist but I find thier comments offensive because i think that those comments are racist in nature. I want them to stop!