A decadent person assumes that the usual values of family, religion, and morality are wrong or irrelevant.
1. Algy tells Jack that a man who marries without having an outside interest (e. g., Bunbury) "has a very tedious time of it." Marriage is not fulfilling, and indeed a few mibnutes after he has met Cecily, to whom he proposes, he tells her about Bunbury.
2. Lady Bracknell, a hypocritical representative of the morality, explains to Algy thet feeling well and acting well rarely go together.
3. Jack is not immune from decadence. Rather than stay at his dull country estate he pretends to have a dissolute elder brother who gets into "scrapes." So he too finds moral life, no matter how much money attends it, stultifying. Assuming a high moral tone does not "conduce to happiness."
4. Cecily is supposed to study German--a language that Lady Bracknell connects with correctness--but finds it hateful. She really wants to meet her Uncle Jack's "wicked elder brother." Lessons are less fun that romance: a decadent choice.
5. Gwendolyn only wants a sham marriage. She asks Jack to look at her loving "especially when other people are present." She says she may "marry often," though she will always love Jack. (Will she?)
There are many other instances, all amusingly put.