The most common and most likely answer to this crossword clue is the 8 letter word SCREW-UP
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More clues leading to the result SCREW-UP
Buddy explains!

The straight part
We know that "fiasco" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fiasco = screw-up.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 SCREW-UP mean?
SCREW-UP noun- A substantial mistake, usually causing problems for more people than just the person or group who made it.
- A person who often makes substantial mistakes; a bungler.
- A person who is mentally or emotionally damaged.