I saw this: "Don't you wish your girlfriend was grammatically correct like me?"
I'm wondering should it be: "Don't you wish your girlfriend was grammatically correct, like me?"
I found this comma guidance online:
That guidance suggests that a comma might be appropriate. Moreover, the same website goes on to say:
Assuming the quip is meant to imply that "your girlfriend" is not grammatically correct (unlike the speaker), that could be a case of "extreme contrast." However, judging by the omitted comma, maybe the contrast isn't so extreme after all.
There is another theory of comma usage, which says that a comma is used to mark a particular kind of intonation dip, which -- since it is an intonation -- is used in English speech to differentiate constituents.
This theory is illustrated by the remarks on comma use by Lewis Thomas in his classic short essay "Notes On Punctuation":
From this theory one may derive this advice:
The "Otherwise" cases often include short idiomatic reduced phrases like don't or like me. Alternatively, these phrases may be separated, as needed, for dramatic effect, like this.
It’s well-known that punctuation can change meaning. A classic example of this is the sentence “A woman without her man is nothing.” With different punctuation, we have, “A woman: without her, man is nothing.” – with antonymous meaning.
In your example, if you put the comma, it means that you, too, are grammatical. If you don’t put the comma, it means that you, too, wish that his girlfriend were grammatical.
Also, I think we all understand that “was” (at least among Americans) is a crude / lazy but common form of the subjunctive “were”, so whether it gets changed to “were” is irrelevant for your question, but since it WAS changed, I used “were” herein.