Around what year would you say that "courtesy and winning ways went out of style, when it was good to be bad and when you cultivated decadence like a taste" (taken from T. Coraghessen Boyle's "Greasy Lake")?
The narrator mentions a key event in history going on around the time of the story, which helps us date the moment, in his opinion, that courtesy and winning ways went out of style. He likens dropping his car keys in the grass at night around Greasy Lake to General Westmoreland's decision to "dig in" at Khe Sanh, referring to them both as "irreversible" tactical errors. Khe Sanh was a battle in the Vietnam War that began early in 1968.
It's not surprising that the narrator would locate 1968 as the year when it became "good to be bad" and he and his friends began to cultivate "decadence." Many historians would mark that year as a turning point in which public opinion against the Vietnam War hardened into virulent opposition. Many movements that had been building for years to address social ills, such as sexism and racism, burst out with renewed vigor. It was a period of upheaval that ranged from campus unrest to assassination. If you compare photographs of young people in 1966 or 1967 against those of 1968, the differences are often startling: teens have gone from neat dresses, ties, jackets, and short, carefully styled hair to jeans, love beads, long hair, and a natural look. The narrator is correct that he and his friends are part of a period of great social change characterized by rebellion and challenges to authority, which he characterizes as "courtesy and winning ways" going out of style.
T. Coraghessen Boyle's "Greasy Lake" opens with the narrator stating that "courtesy and winning ways" are "out of style." The narrator goes on to state that "it was good to be bad," and people "cultivated a decadence like a taste." What this means is that people were no longer courteous, and it was considered appropriate to be bad. People, on top of being bad and without courtesy, were embracing the decline of a culture of morals.
In regards to what year this happened in reality, different people will have different answer to this. Some adolescents may not recognize that courtesy has disappeared. While the bad boy attitude has always been around, the lack of morality and courteous natures have not.
I would suggest that courtesy went out of style with chivalry. As feminists desired to open their own doors, pay for their own meals, and be a part of the work force, courteous behaviors have been on the decline. While not everyone will agree with me, I do believe that morality and courtesy began to decline as women desired equality and power.
(On a side note, I am sure that some people may misunderstand my answer and accuse me of anti-feminist ideologies. This is not my intent. Instead, I am only offering my educated answer regarding the point when courtesy began to decline. Although the story was written in 1985, courtsey and morality began to decline far before that.)