The most common and most likely answer to this crossword clue is the 5 letter word PRATS
P
R
A
T
S
Buddy explains!
The straight part
We know that "First in perspicacity? Nonsense!" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case first in perspicacity? nonsense! = prats.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 PRATS mean?
PRATS noun- A cunning or mischievous trick; a prank, a joke.
- A buttock, or the buttocks; a person's bottom.
- A fool.
- The female genitals.