Obviously the title above is meant to be sarcastic because summer ending is not a happy occasion in the slightest. Unless you really love fall. In which case I would wish you a happy return of the pumpkin spice latte.
In any case, here’s an article about the origin of the fashion principle which bans wearing white after labor day. While the conclusion they offer in this article says if the queen of England thinks it’s OK to do it then we can all do it, I personally have never based my fashion choices on those the queen makes.So take a look and decide for yourself if this rule is made to be broken.