The most common and most likely answer to this crossword clue is the 6 letter word CRUSTY
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Buddy explains!

The straight part
We know that "Bad-tempered" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case bad-tempered = crusty.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 CRUSTY mean?
CRUSTY noun- A tramp or homeless young person with poor cleanliness.
- Dried eye mucus.
- A member of an urban subculture with roots in punk and grebo, characterized by antiestablishment attitudes and an unkempt appearance.
- Having a crust, especially a thick one.
- (of a person or behavior) Short-tempered and gruff but, sometimes, with a harmless or benign inner nature.
- Of very low quality.