The most common and most likely answer to this crossword clue is the 6 letter word COQUET
I've seen this crossword clue in The Guardian
C
O
Q
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More clues leading to the result COQUET
Buddy explains!

The straight part
We know that "Flirt" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case flirt = coquet.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 COQUET mean?
COQUET noun- A flirtatious female; a coquette.
- A flirtatious male.
- To act as a flirt or coquet.
- To waste time; to dally.
- To attempt to attract the notice, admiration, or love of; to treat with a show of tenderness or regard, with a view to deceive and disappoint; to lead on.