The most common and most likely answer to this crossword clue is the 9 letter word EARTHIEST
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More clues leading to the result EARTHIEST
Buddy explains!

The straight part
We know that "most vulgar" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case most vulgar = earthiest.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 EARTHIEST mean?
EARTHIEST adjective- Resembling dirt or soil (i.e. earth).
- Down-to-earth, not artificial, natural.
- Coarse and unrefined, crude.
- Like or resembling the earth or of the earth.
- Covered with earth (mud, dirt).