Young Koreans are no longer merely fitting into public spaces according to social roles dictated by age or student status, but by a feeling of entitlement to occupy spaces according to their needs as enabled by an equality-as-consumer. It's not a pure egalitarian ideal as equality-as-citizens. That's where the new obsession with fashion comes in for Korea. Equality-as-consumers, expression-of-identity as consumers, combined with sartorial desire.
This is also the case with younger women who are dressing according to the way they like and also smoking in public, since nowadays one could scarcely imagine an older man scolding and chastising a young lady for smoking, whereas only about 20 years ago, one could have scarcely imagined a young woman of any disposition smoking openly and freely in public on an open street in an uncovered area.
I feel the same holds true for kissing in public and other such displays of obvious and unfettered affection in places where anyone might see. This, along with the fact that there are many specific narratives and representations of people doing just such things, to the point that it has become socialized as okay, especially in the way it fits into the narratives of one's own life as a couple as that might match the narrative of the romantic comedy or that of two people having enough affection for one another to flout popular convention.
In that sense, kissing becomes a public, declatory act, similar to that of wearing matching items of clothing in public, which was popular in Korean culture for newlyweds only, and was a signifier of being such, also around 20 years ago.
Indeed, The way that Koreans as citizen-subjects conducted themselves in public spaces around the time UB40 was popular is indeed completely different from the way that Koreans as consumer-subjects do so today. .