The most common and most likely answer to this crossword clue is the 17 letter word THEÂ FACTSÂ OFÂ LIFE
I've seen this crossword clue in The Guardian
T
H
E
Â
F
A
C
T
S
Â
O
F
Â
L
I
F
E
Buddy explains!
The straight part
We know that "Straight instruction" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case straight instruction = the facts of life.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.