I think one problem is the attitude Lois pointed out of the woman being embarrassed and not saying anything. I don’t care whether the person telling the joke is putting down another race or ethnicity or his/her own, it’s up to the listener to do what s/he can to inhibit further junk like that. I haven’t heard any recently, but when I was younger and someone would tell such a joke, I’d always respond with something like, “Wow, that’s a really stupid joke. Do you feel so inferior that you have to tell jokes that put down whole classes of people?”
The funny thing was that while I may have lost the friendship of the teller, often afterwards two or three of the others would agree with me. I’m sure I didn’t change the person, but if that prevented him/her from telling it in the future, it was worth me doing that.
Something interesting in this regards http://www.psychologytoday.com/blog/without-prejudice/201307/dehumanizing-others-is-no-joke