"disgruntled about" is correct and can be used in written English.
An example sentence using this phrase could be: "The workers were disgruntled about the changes to their benefits package."
He's not disgruntled about the results".
They have much to be disgruntled about.
The tree was a kind of anchor for the people, and they were disgruntled about it.
"You think he would have been disgruntled about that," Mr. Ackley said.
Around 2004, Major Hasan started feeling disgruntled about the Army, relatives said.
She went on: "We are constantly used to Spain being disgruntled about one thing or another.
The disgruntled complained about cripplingly long hours, intense competition and the impersonality of the biggest firms (some with more than 3,000 lawyers).
A further digression: a good few years ago, I was privileged to attend the very first Devoted & Disgruntled conversation about the future of theatre.
Pew's report details some comments it gathered from participants who were not willing to accept this trade-off — including plenty of disgruntled views about the volume of marketing content they are encountering on such sites these days.
You're irritated and about to reply with a disgruntled response, well, how about this to bide you some time: "I'm not sure I understand.
Yet it was not only many ethnic-Chinese voters (about a quarter of the population) and, especially, disgruntled ethnic Indians (about 8%) who deserted the National Front.
