The most common and most likely answer to this crossword clue is the 7 letter word GROUCHY
I've seen this crossword clue in The Guardian
G
R
O
U
C
H
Y
More clues leading to the result GROUCHY
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 = grouchy.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 GROUCHY mean?
GROUCHY adjective- (originally student slang) Irritable; easily upset; angry; tending to complain.