The most common and most likely answer to this crossword clue is the 13 letter word OLD-FASHIONED
I've seen this crossword clue in The Times
O
L
D
-
F
A
S
H
I
O
N
E
D
More clues leading to the result OLD-FASHIONED
Buddy explains!
The straight part
We know that "not with it" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case not with it = old-fashioned.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does OLD-FASHIONED mean?
OLD-FASHIONED noun- A cocktail made by muddling sugar with bitters and adding whiskey or, less commonly, brandy, served with a twist of citrus rind.
- Of a thing, outdated or no longer in vogue.
- Of a person, preferring the customs of earlier times.