The most common and most likely answer to this crossword clue is the 11 letter word COMPORTMENT
I've seen this crossword clue in The Times
C
O
M
P
O
R
T
M
E
N
T
More clues leading to the result COMPORTMENT
Buddy explains!

The straight part
We know that "personal manner" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case personal manner = comportment.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 COMPORTMENT mean?
COMPORTMENT noun- The manner in which one behaves or conducts oneself
- Deportment, bearing