The most common and most likely answer to this crossword clue is the 3 plus 1 plus 3 plus 7 letter word SET A BAD EXAMPLE
I've seen this crossword clue in The Guardian
S
E
T
A
B
A
D
E
X
A
M
P
L
E
Buddy explains!
The straight part
We know that "to encourage antisocial behaviour" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case to encourage antisocial behaviour = set a bad example.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.