The most common and most likely answer to this crossword clue is the 12 letter word FOOLHARDIEST
I've seen this crossword clue in Financial Times
F
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Buddy explains!
The straight part
We know that "most bold and stupid" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case most bold and stupid = foolhardiest.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 FOOLHARDIEST mean?
FOOLHARDIEST adjective- Marked by unthinking recklessness with disregard for danger; boldly rash; hotheaded.