In Louisiana, at a clambake on college grounds, a senior professor had overheard a sophomore warning some freshmen about the chiggers -- insects that burrow under your skin; a local hazard. Without stopping to think, the professor had blurted out a foolish witticism: "We're not allowed to call them chiggers anymore," he said, guffawing, "We have to call them chegroes."
... The matter was brought before the Disciplinary Committee, and we agreed unanimously that the joke was a speech act showing complicit contempt for minority students.
The Horned Man by James Lasdun
There's no telling what will make people upset. The solution seems to be to make insipid, bland, boring, and as non-controversial as one can possibly make it. And your story reminds me why one has to watch themselves when it the occasion arises to tell a joke. Finding something funny is verboten to the P.C crowd. It seems the business of ensuring no one's feelings ever get hurt have been taken too far.