The most common and most likely answer to this crossword clue is the 5 letter word CHURL
I've seen this crossword clue in The Guardian
C
H
U
R
L
Buddy explains!

The straight part
We know that "rude one" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case rude one = churl.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 CHURL mean?
CHURL noun- A rustic; a countryman or labourer; a free peasant (as opposed to a serf).
- A rough, surly, ill-bred person; a boor.
- A selfish miser; an illiberal person; a niggard.
- (Theodism) A freedman, ranked below a thane but above a thrall.