Why slap is out of order — that's how bad-tempered sort reacts (9)

I believe the answer is:

waspishly

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'order that's how bad-tempered sort reacts' is the definition.
I can't judge whether this definition defines the answer.

'why slap is out' is the wordplay.
'out' indicates an anagram (out can mean wrong or inaccurate).
'why'+'slap'+'is'='whyslapis'
'whyslapis' is an anagram of 'WASPISHLY'.

'of' is the link.

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I've seen this clue in The Guardian.

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