The most common and most likely answer to this crossword clue is the 8 letter word IMPOLITE
I've seen this crossword clue in The Guardian
I
M
P
O
L
I
T
E
More clues leading to the result IMPOLITE
- Ill-mannered urchin drunk in Dover from time to time
- Trouble-maker having nothing, half-educated, loutish
- Rude little blighter to lie outrageously
- Rude young offender vandalised toilet largely
- Discourteous? I am the complete opposite
- Naughty child to lie when in trouble, being insolent
- The setter’s humourless, healthy and rude
- Independent person elected to lie badly, being insolent
- Rude child, to lie deviously
- Bad-mannered male, Italian, entering bar after one
Buddy explains!

The straight part
We know that "insolent" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case insolent = impolite.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 IMPOLITE mean?
IMPOLITE adjective- Not polite; not of polished manners; wanting in good manners.