The most common and most likely answer to this crossword clue is the 8 letter word VIOLATOR
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Buddy explains!
The straight part
We know that "One might vandalise" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one might vandalise = violator.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 VIOLATOR mean?
VIOLATOR noun- One who violates (a rule, a boundary, another person's body, etc.); offender
- In the publishing and packaging industries, a visual element that intentionally "violates" the underlying design, such as a starburst, color bar or "splat" on a product package or magazine cover intended to attract special attention.