Coming for my neck
(A): A well-timed, but unintentional roast; stating the allegedly true facts of a given situation; speaking truth on a matter for which you may have no prior knowledge, but it is extremely relevant to a given situation.

(B): The response to a well-timed statement and/or unintentional roast. Part of a much larger sentence structure that responds with humor to the revelation of previously unknown facts or truth that is relevant to a given situation.
Definition (A) -

Person A: Aye, bro, you need coffee or something? You a asshole when you ain't got your coffee

Person B: Damn, bro! Why you stay coming for my neck like that?