It's not a rule on paper that decides what's allowed, it's a human with their own history and beliefs who has that authority - if you can't board the flight it doesn't exactly help you that the airline apologizes to you afterwards because the decision to throw you off was clearly wrong.

People get thrown off flights [for][1] [the][2] [most][3] [ridiculous][4] [reasons][5], so my personal advice is: Dress like you always do, don't bother with the small chance that you'll meet someone wanting to abuse their power, and if bad luck hits you, revel in the fact that you now have a good story to tell, while the power-tripping simpleton who threw you off the plane is probably getting fired for it.


  [1]: http://www.iflscience.com/editors-blog/economist-gets-interrogated-writing-equations-airplane
  [2]: http://www.foxnews.com/travel/2016/02/29/175lbs-passenger-removed-from-flight-for-being-too-heavy.html
  [3]: http://www.theguardian.com/uk-news/2016/mar/03/man-removed-easyjet-flight-luton-prayer-message-phone
  [4]: http://edition.cnn.com/2016/01/18/us/muslims-sikh-sue-airline/
  [5]: http://edition.cnn.com/2016/04/17/us/southwest-muslim-passenger-removed/