The most common and most likely answer to this crossword clue is the 10 letter word NEEDLESSLY
I've seen this crossword clue in The Times
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More clues leading to the result NEEDLESSLY
- Provokes Sally occasionally for no reason
- Hype’s devious in a gratuitous way
- for no good reason
- Annoys, coming over underhand for no reason
- Pointers tricky without point
- Annoys son unloading lorry for no reason
- Hype’s deceptive? Not necessarily
- Irritates, having got roguish without any necessity
- Irritates Christopher, perhaps, without having to
- Irritates actor for no reason.
Buddy explains!

The straight part
We know that "for no reason" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case for no reason = needlessly.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 NEEDLESSLY mean?
NEEDLESSLY adverb- In a needless manner
- To a degree or extent beyond what is needed
- Without need