The most common and most likely answer to this crossword clue is the 10 letter word IMPRUDENCE
I've seen this crossword clue in The Sunday Telegraph
I
M
P
R
U
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E
More clues leading to the result IMPRUDENCE
- Menu priced incorrectly could show this
- Daring to poke right inside lip
- Presumption about Republican's indiscretion
- Presumption about Republican’s lack of discretion
- Rascal’s discourteous then nice, not one to show lack of caution
- Cheek concealing Republican indiscretion
- Folly of Romeo interrupting disrespectful behaviour
- Rashness and cheek? That’s about right
- Audacity about right, showing lack of judgment
- Recipe soaked in sauce shows lack of judgment
Buddy explains!
The straight part
We know that "stupid behaviour" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case stupid behaviour = imprudence.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.