There is a way. Find an obvious example where the media lied about something they're an expert on. It can be a lie about something in their field, their community, about people they know, or a part of history upon which they're well studied. Show them, let them condemn it and then ask, "If they could get this wrong then what else have they gotten wrong?"

This is exactly what started me on the path to discovering that the media is full of propaganda and that our government is corrupt.