The most common and most likely answer to this crossword clue is the 5 letter word PICKY
I've seen this crossword clue in The Guardian
P
I
C
K
Y
More clues leading to the result PICKY
Buddy explains!

The straight part
We know that "pernickety" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case pernickety = picky.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 PICKY mean?
PICKY noun- A picture.
- Fussy; particular; demanding to have things just right.