I wonder if what is being called lazy here is a misidentification of what that form of speech you’ve used as an example really is? I’d suggest that rather than being lazy, it’s a form of code-switching which recognises a specific environment, that is, being with an group of people where the question of going to to the beach is likely to arise, i.e. in an informal, friendly situation.
In that kind of circumstance, a crisply articulated, “No thank you, I do not wish to go to the beach”, would possibly be the inappropriate mode, and likely to get a reply like, “yeah, what’s wrong with you.”? So I’d argue that in that circumstance it’s not about laziness, it’s about using a mode of speech appropriate to the moment, code-switching.
Again, your example from The Sopranos was interesting. Where I used to live was a working class, inner-city industrial suburb, with a large population of Greek and Italian migrants, many of whom had arrived post-World War II. That kind of accent was very typical of my students, and sufficiently common that it was recognised as a “Westie” or “Bogan” accent in other parts of the city.
There was a distinct class bias against the accent, and people from those suburbs who moved “up” tended to lose it, because it was seen, with no justification, as an indication of lower intelligence, presumably because of its working-class origins.
Certainly the accent wasn’t about laziness, that was how many people in lived in the area spoke, my students had the accent because that’s how their friends and parents spoke. For some of them, the issue become a difficult one if they chose to embrace a more “standard” accent because they were sometimes seen as “selling out”, turning their backs on their working class/immigrant origins and aspiring to be middle-class, or, in Bogan, “up themselves”.
For many people who live in those suburbs, their identification with that background is very strong, and the way they speak is a means of identification with their families and peers. Given the amount of racism “wogs” copped from Anglo-Australians, not to mention the amount of prejudice against the Western suburbs, I don’t see that it’s at all surprising that even in adulthood many would choose to keep the accent, as an act of defiance and identification.
For a teenager, mumbling, shuffling and slouching are probably not really about laziness, except in so far as adults choose to characterise them in that way. Kids have lots of energy, they don’t need to conserve it. It’s about being a teenager, identifying with their peers, using movement and voice to be part of the group. It’s a kind of defiance, “I am a kid, and this is how kids behave”.
If an adult says to a teenager, “sit up straight, don’t be lazy”, unless they’re posture maniacs, they’re really saying, “be more like an adult, behave in the way I think is consistent with my image of adult behaviour, be more like me”. “Lazy” is really just a code, when what is really going on is behaviour modification and control.
The thing is, as humans we’re hardwired for language, it’s who and what we are, so the ways in which we use language are very complex, so embedded in our social and cultural context that often we don’t even realise what is going on. Although we talk a lot, quite a bit of what we are saying isn’t about the meanings of the words and sentences we’re using, but metacommunication, discourses which build and define power, relationships and culture…
If you’re interested in this stuff, a search for “speech codes”, semiotics and “communication theory” will find lots of references.