This achievement is earned during the 'Wicked Eyes and Wicked Hearts' quest. It requires you to finish the quest with full court support (100/100).
You can get support through dialogue with court members. Find people with a speech bubble and
save before talking (even if not everyone has something meaningfull to say) - obviously use multiple saves throughout this quest. Play your cards close to your chest, and never be blunt or you'll lose approval. Small amounts can be earned by finding Caprice coins and throwing them into the fountain.
When exploring areas outside the main attraction, be quick, for you will lose approval constantly.
If you enter the ball room after the bell rings for a second time you'll gain approval for being 'fashinonably late'.
You can earn a large amount of approval during the dance with the Duchess if you always pick the center-right option.
Finally, when -
*** Spoiler - click to reveal ***deciding who get's to live and who to die, pick the option of avoiding blood shed and calling the duchess out. I had 98/100 at this point but this gave me the achievement.
*EDIT* Since people seem to fail to understand: Picking any other choice than the peaceful one described in the spoilers will lower your score (and void the achievement), while making that choice will increase your score. This one final choice will influence your score by +/- 10 points, but it won't be displayed. Which is why people with 100/100 didn't get the achievement when picking a fight, and people with 90/100 got it when choosing the peaceful option.
I finished the quest while finding only four Hallas, and learning less than half of the scandals and secrets, so those aren't required to neither finishing the quest nor getting this achievement.