The most common and most likely answer to this crossword clue is the 5 letter word SNOBS
I've seen this crossword clue in Financial Times
S
N
O
B
S
Buddy explains!
The straight part
We know that "Pretentious persons" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case pretentious persons = snobs.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 SNOBS mean?
SNOBS noun- A person who wishes to be seen as a member of the upper classes and who looks down on those perceived to have inferior or unrefined tastes.
- A cobbler or shoemaker.
- A member of the lower classes; a commoner.
- A workman who works for lower wages than his fellows, or who will not join a strike.
- (Cambridge University) A townsman, as opposed to a gownsman.