The most common and most likely answer to this crossword clue is the 13 letter word INCONSIDERATE
I've seen this crossword clue in Financial Times
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More clues leading to the result INCONSIDERATE
- Unfortunate incident arose, being careless
- Insincere toad sadly thinking of no one else?
- Unfortunate incident arose, not thinking
- Selfish Indian opener is a contender, surprisingly
- Selfish criminal appropriately incarcerated by judge?
- Cross about North Carolina following rules? That’s unthinking
- New direction for stopping bad reaction and rash
- Behind bars having committed swindle – judge intolerant
- ‘Extraordinary rendition’ case is unkind
- Trick admitted by home team deem to be ‘thoughtless’
Buddy explains!

The straight part
We know that "rash" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case rash = inconsiderate.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 INCONSIDERATE mean?
INCONSIDERATE adjective- Not considerate of others.
- Not giving enough consideration to one's actions, conclusions, etc.; acting too quickly without considering the risks and consequences.
- Resulting from insufficient consideration.
- Of too little value to be considered.