The most common and most likely answer to this crossword clue is the 10 letter word NARCISSISM
I've seen this crossword clue in The Daily Telegraph
N
A
R
C
I
S
S
I
S
M
More clues leading to the result NARCISSISM
- Some regularly supporting blooms, displaying vanity
- Man’s crisis shattered his enormous self- regard
- You’ll really admire yourself having this combination of bloomers and S&M
- Such vanity, writing about lying under daffodils!
- Achieving 50% reduction of narcotic issues in smug self-admiration
- Self-loving unstable man’s crisis
- Man’s crisis could come from such self-interest
- Man’s crisis: awful vanity
Buddy explains!

The straight part
We know that "self-interest" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case self-interest = narcissism.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 NARCISSISM mean?
NARCISSISM noun- Excessive love of oneself.
- Sexual desire for one's own body.