see the title made me think you were going to talk about positive discrimination, or whatever the fancy word is nowadays.
If they're taking the piss, they're taking the piss and you're well within your rights to stab them with a verbal spear in response. Then again, when it comes to humour a lot of people enjoy jokes about taboo things. Why do you think toilet humour is so funny as a kid? Cuz no one talked about it. Then it goes on with age and we find other taboos in conversation. Sex, violence and, yes, racial issues.
The main thing I look out for is the spirit of the the conversation. My media teacher has an indian heritage and it shows in his skin colour and facial features. Whilst watching the film "The Help" about black maids & nannys in america he says: "That's my job too. Taking care of white babies." You could probably find something offensive in there. Nobody did because it's not like he actually wanted to offend anyone and we weren't looking to be offended.