The most common and most likely answer to this crossword clue is the 11 letter word IMPERTINENT
I've seen this crossword clue in The Daily Telegraph
I
M
P
E
R
T
I
N
E
N
T
More clues leading to the result IMPERTINENT
- I am flourishing because of special branch of medicine being fresh
- Saucy material that one male suppresses
- Shameless little devil on internet misbehaving
- Fresh mint I repent getting chopped up
- Rude writer is to the point
- Cheeky troublemaker has abused internet
- Rude material suppressed by films regularly
- I am apt to be cheeky
- Cheeky brat in hospital department, inspiring regret regularly
Buddy explains!

The straight part
We know that "Rude" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case rude = impertinent.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 IMPERTINENT mean?
IMPERTINENT noun- An impertinent individual.
- Insolent, ill-mannered
- Irrelevant (opposite of pertinent)