When do you think "jokes" go to far?

just read a question that made a joke about 9/11.I couldn't beleive someone made a joke about somethin so frickin horrible and scary.Yet some people were goin right along with it and laughin it off And just today my friend makes this black joke and expects me to laugh,and i told him,why the hell do you expect me to laugh at you mocking my race? ((idiot!))and then he goes on basically calling me TOO serious.I mean,is nothing sacred anymore? do we joke about every got darn thing?!when do you think too far is too far?