The most common and most likely answer to this crossword clue is the 7 letter word FINICKY
I've seen this crossword clue in The Times
F
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Buddy explains!

The straight part
We know that "of fussy disposition" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case of fussy disposition = finicky.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 FINICKY mean?
FINICKY adjective- (of a person) Fastidious and fussy; difficult to please; exacting, especially about details.
- Demanding; requiring above-normal care.