Medjugorje from the Pulpit

It depends on the context. If the priest was insisting that what the Virgin Mary said in that context was to believed by the faithful, then he would be in the wrong. If the priest was simply using a story to illustrate a larger point, it would probably be okay, even if a bit problematic. The reason it would be problematic is that the Church has not formally approved the alleged apparitions in Medjugorje—indeed, the local bishop has declared not of supernatural nature—so using it to illustrate the Faith is not the best choice.