The most common and most likely answer to this crossword clue is the 10 letter word BLUSTERING
I've seen this crossword clue in The Guardian
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Buddy explains!
The straight part
We know that "Swaggering" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case swaggering = blustering.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 BLUSTERING mean?
BLUSTERING verb- To speak or protest loudly.
- To act or speak in an unduly threatening manner.
- To blow in strong or sudden gusts.
- A noisy blowing, as of a blast of wind.
- Swaggering; braggartry; noisy pretension.
- Engaged in or involving the process of blustering, speaking or protesting loudly.
- Pompous or arrogant in one's speech or bearing.
- Very windy; (of wind) blowing very strongly, blustery.