Here are some synonyms for "disgruntled":
* Unhappy
* Dissatisfied
* Resentful
* Annoyed
* Frustrated
* Discontented
* Displeased
* Grumbling
* Bitter
* Unfulfilled
Example:
* "The employees were disgruntled with their low wages and poor working conditions."
* "The customer was disgruntled after waiting for an hour to be served."
Let me know if you'd like more examples or have any other questions!