Grammar at its best promotes clear communication but more often is used as a social tool of control and exclusion. When you are already talking to people within your in-group, that impulse isn’t necessary.
On some level. Thing is it is visible and everybody knows what the standards are, social mobility is possible under the sign of grammar.
If the game is wearing a $20k watch or understanding the covert signs of status that you might find in a particular community, that's something different.
According to the wide definition of grammar, everyone uses some grammar, but nevertheless it's not a category error to say "*this sentence got grammar mistake".
When we speak about the grammar for a language/dialect we imply a prescribed "correct" grammar for a particular community of speakers.
> speak about the grammar for a language/dialect we imply a prescribed "correct" grammar
Not prescribed, rather observed. At least in English where there is no language authority and dictionaries present usage.
The situation is even stranger in Norway where there is a prescribed form but where dialects have essentially equal rights so that the prescription really applies only to formal written Norwegian.
From what I experienced, "proper" English grammar is absolutely prescribed at schools, and "poor grammar" will consistently and very predictably get you point deductions, regardless of whether linguists would accept your grammar as valid.
If the game is wearing a $20k watch or understanding the covert signs of status that you might find in a particular community, that's something different.