Wear the tie for your first checkride at a new airline. Not for general sim lessons with check airmen/instructors. Once you're on with the airline you'll never have to wear it again for a training event. I have heard more than one APD give a guy grief for not wearing one, however those same ones will tell you to take it off later after the introductions usually. Plus whats the big deal about wearing one? as a pilot you'll be wearing one every day anyways.