The most common and most likely answer to this crossword clue is the 5 letter word GOOFY
I've seen this crossword clue in The Times
G
O
O
F
Y
Buddy explains!
The straight part
We know that "imbecile" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case imbecile = goofy.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 GOOFY mean?
GOOFY adjective- Silly, quirky
- One who rides with the right foot forward.
- Riding with the right foot forward.