From The National Post:
Last August, a blogger in Cincinnati going by the name CincyBlurg reported that a black friend from the southeastern U.S. had recently discovered that she was being called a Canadian. "She told me a story of when she was working in a shop in the South and she overheard some of her customers complaining that they were always waited on by a Canadian at that place. She didn't understand what they were talking about and assumed they must be talking about someone else," the blogger wrote.
"After this happened several times with different patrons, she mentioned it to one of her co-workers. He told her that ‘Canadian' was the new derogatory term that racist Southerners were using to describe persons they would have previously referred to [with the N-word.]"
A similar case in Kansas City was reported last year on a Listserv, or electronic mailing list, used by linguistics experts. A University of Kansas linguist said that a waitress friend reported that "fellow workers used to use a name for inner-city families that were known to not leave a tip: Canadians. ‘Hey, we have a table of Canadians.... They're all yours.' "