The most common and most likely answer to this crossword clue is the 9 letter word STRAIGHTS
I've seen this crossword clue in The Guardian
S
T
R
A
I
G
H
T
S
Buddy explains!

The straight part
We know that "they’re not bent" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case they’re not bent = straights.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 STRAIGHTS mean?
STRAIGHTS noun- Something that is not crooked or bent such as a part of a road or track.
- Five cards in sequence.
- A heterosexual.
- A normal person; someone in mainstream society.
- A cigarette, particularly one containing tobacco instead of marijuana. Also straighter.
- To straighten.