Formal:
* Displeased: This is the most direct opposite, indicating a negative emotional state.
* Unhappy: A more general term for a lack of joy or contentment.
* Dissatisfied: This suggests a lack of fulfillment or meeting of expectations.
* Offended: This implies that something has caused negative feelings or hurt.
Informal:
* Unhappy: A simple and common word.
* Grumpy: Indicates a bad mood or irritability.
* Angry: A strong negative emotion.
* Disgruntled: A sense of dissatisfaction or resentment.
* Bummed: A casual word for feeling disappointed or let down.
Other options:
* Sad: A general term for experiencing negative emotions.
* Depressed: A more severe state of sadness and hopelessness.
* Apathetic: Lacking interest or emotion.
The best word to use will depend on the specific situation and the desired level of formality.