The most common and most likely answer to this crossword clue is the 3 letter word CAD
I've seen this crossword clue in The Guardian
C
A
D
More clues leading to the result CAD
Buddy explains!

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 CAD mean?
CAD noun- A low-bred, presuming person; a mean, vulgar fellow.
- A person who stands at the door of an omnibus to open and shut it, and to receive fares; an idle hanger-on about innyards.