The most common and most likely answer to this crossword clue is the 6 plus 3 plus 6 letter word DENNIS THE MENACE
I've seen this crossword clue in The Guardian
D
E
N
N
I
S
T
H
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M
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N
A
C
E
More clues leading to the result DENNIS THE MENACE
- Comic character in the end’s beaten danger
- Cartoon character with naughty he-man tendencies
- He’s indecent! Name unholy terror who’s stripped
- 3’s lively dance includes Olympian idea
- Walter’s nemesis incensed me then, a rowdy
- Made a mistake when recalling topic, one involving name of a cartoon character
- Did wrong backing main idea by new, wicked scamp
- Troublesome boy developing he-man tendencies
Buddy explains!
The straight part
We know that "Troublesome boy" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case troublesome boy = dennis the menace.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.