Is the phrase
[all] up in $POSSESSIVE_PRONOUN grill
which is synonymous with the figure of speech
in one’s face
an automotive metaphor?
If so, would it be more correct to spell the last word “grille”?
If not, what does the phrase mean?
“Grill” refers to jewelry that some people wear on their teeth. It is prevalent in hip-hop culture, where it is a way to show off one’s “bling” – or wealth – when you smile. Your synonymous phrase is correct.
Both spellings of the word are related etymologically, as “grill” is merely a shortened form of “grille” (according to etymonline)
I think it’s safe to assume that this meaning of grill is related to the cooking implement and is similar in that they are both made of metal. See comment below by ghoppe.