The most common and most likely answer to this crossword clue is the 8 letter word RESENTED
I've seen this crossword clue in The Times
R
E
S
E
N
T
E
D
Buddy explains!

The straight part
We know that "Was indignant about" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case was indignant about = resented.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 RESENTED mean?
RESENTED verb- To feel resentment over; to consider as an affront.
- To express displeasure or indignation at.
- To be sensible of; to feel.
- In a positive sense, to take well; to receive with satisfaction.
- To recognize; to perceive, especially as if by smelling; -- associated in meaning with sent, the older spelling of scent, to smell. See resent (intransitive verb).
- To give forth an odor; to smell; to savor.