Simple:
* The customer was indignant about the poor service he received.
* She was indignant at the injustice of the situation.
With more context:
* The politician's indignant tone made it clear he wouldn't back down from the accusation.
* The children were indignant when their parents cancelled their trip to the amusement park.
* The teacher was indignant that the students had cheated on the test.
Figurative:
* The air crackled with indignant whispers after the news of the scandal broke.
Using different parts of speech:
* Her indignation at the unfair treatment was palpable. (noun)
* He indignantly refused to apologize. (adverb)
* The indignant look on his face spoke volumes. (adjective)
Remember, "indignant" implies strong displeasure or anger at something perceived as unfair or unjust.