Back in the day, he never talked to you straight, as in not in code?
It means: He always talked to you in code, never straight, didn't he?.
This is the use of a double negative in English:
If we remove the as in, we get:
He never talked to you not in code, [right]?.
as in is used to clarify a thought.
You never liked shitty movies, did you? As in shitty horror movies.
Double negatives are used in English at times in conversation to clarify a sentence that is in the negative.
You never did not like movies, did you?
is the same as; You always liked movies, didn't you?
It is used for emphasis....or to fix an ambiguity.