The most common and most likely answer to this crossword clue is the 9 letter word CARPETING
I've seen this crossword clue in The Daily Telegraph
C
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More clues leading to the result CARPETING
Buddy explains!

The straight part
We know that "dressing down" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case dressing down = carpeting.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 CARPETING mean?
CARPETING verb- To lay carpet, or to have carpet installed, in an area.
- To substantially cover something, as a carpet does; to blanket something.
- To reprimand.
- Carpet or a piece of carpet, especially when speaking of installation or removal.
- Cloth or materials for carpets.
- A severe reprimand or telling-off.