There is nothing wrong with saying that you are a prophet, if you are a prophet, just as there is nothing wrong with saying that you are a teacher, a preacher, an evangel, or an emmissary. We refer to Jerimiah as "The prophet Jerimiah," just as we refer to Paul as "The Apostle Paul," to distinguish them from others. The same thing pertains to "John the Baptist," and "John the Apostle." Elijah, for example, very often used the term "so he will know that there is a prophet in Israel" as his reason for healing--this, of course, would be very well rejected if spoken today.
But when a man insists on being called "Prophet Mike," or "Pastor Mike," for that matter, he is more interested in being recognized than in doing the work of Yahweh. Prophets don't care if you address them with a title. False prophets do. While you do see Jerimiah, Ezekiel, or Elijah insisting on the words of Yahweh, you don't see any of them insisting that people refer to them as "Prophet Elijah" in passing every time they address them. This ressembles the word "Rabbi" among the pharisees and scribes moreso than it does "Prophet" with the prophets of the Scriptures. It's ok to call a prophet "Prophet," especially when you don't know his name, but it's a sign of falsehood to insist that people recognize you by your alledged function all of the time.