The most common and most likely answer to this crossword clue is the 10 letter word MISCONDUCT
I've seen this crossword clue in The Daily Telegraph
M
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S
C
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Buddy explains!

The straight part
We know that "bad behaviour" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case bad behaviour = misconduct.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 MISCONDUCT mean?
MISCONDUCT noun- Behavior that is considered to be unacceptable.
- To mismanage.
- To behave inappropriately, to misbehave.
- To act improperly.