The most common and most likely answer to this crossword clue is the 11 letter word METROSEXUAL
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Buddy explains!
The straight part
We know that "Modern man" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case modern man = metrosexual.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 METROSEXUAL mean?
METROSEXUAL noun- A man — typically urban, heterosexual and affluent — who is concerned with personal appearance, such as personal grooming, fashion, and aesthetics in general.
- A heterosexual man who is seen, sociologically, as having attributes common to homosexuals.
- Of or relating to a metrosexual or the metrosexual lifestyle.