Well, I must confess I don't find this ridiculous... Or I should say I'm a bit ridiculous myself, because I find all these questions of Etiquette rather fascinating!
But it was a typically french obsession. If you read the Mémoires of Saint-Simon, you're astounded how he can write ten or twenty pages about an armchair to give or not to give to this prince, when he's in front of this other prince, more or less high-ranking than the first, and so on (read for example the page about the visit of the duke of Lorraine in Paris, to see his brother-in-law the Regent).
There is also a page very interesting in the Mémoires of Mme de Boigne, about Louis XVIII's death.
Before Louis XVIII's death, the duchess of Angoulême was more high-ranking than her husband, because she was daughter of a King (Louis XVI), and her husband was just the nephew of the King. Then, like for Marie-Amélie and Louis-Philippe, the duchess of Angoulême always was going before her husband when they were in front of a door (but, slight difference, the door was always completely open for the duke too, because the rank difference was less distant between the duke and the duchess of Angoulême, than between Louis-Philippe and Marie-Amélie : the Angoulême were daughter/nephew of Kings, the Orléans were daughter/only far descendant of Kings).
And this day, all the royal family was assembled in Louis XVIII's bedroom to assist to his death. And the King died. The duchess of Angoulême liked his uncle very much, and was in tears. She gone with her husband to leave the bedroom, and was on the brink of going through the door before her husband, like she always had done before.
But at this moment, she remembered that since a few minutes, her husband was, like her, the son of a King (the new king, Charles X, Louis XVIII's brother), but moreover son of the reigning King, then now more high than her. So she stopped immediately and moved back, and said to her husband, through her tears : "You go first, Monsieur le dauphin!"
Mme de Boigne, seeing this, was amazed, because she could not understand how the duchess of Angoulême, who was completely distressed, could in the same time never forget the minor detail of the Etiquette...
