My dissertation director asks the best questions.
Once, when I made some unsupported assertion, he just said "Really?" and nothing else. I figured out pretty quickly that I needed to detail my evidence.
So, my response to the "Blacks and Mexicans" screw up the washers is "Really? What did you see? Did it actually break? And no one white has ever done that? If you didn't see it, are you sure you are right?"
One can also go with a Socratic strategy. "Really? They don't know how to act? How should we act? Are you an expert on good behavior? Will you educate me?"
That look. "You know what I'm talking about." But of course you don't. You'll need them to explain what they mean fully, and in detail. . .
I've failed at talking to racists - I'm not good at it, so take these suggestions with a grain of salt. (Or as a fantasy or something that I'd do in a dream or a movie.) They get offended and upset when they can't answer. One even stopped speaking to me, which wasn't my intended result, but I'm enjoying it over here where it's quiet.
Best of luck. Fun article! --SW