不機嫌

1. Origins, structure, and basic meaning

• Structure: 不機嫌, read ふきげん, adds the negative element 不 to 機嫌 (mood).
• Basic usage: It describes being displeased or in a bad mood and behaves like a na-adjective.

2. Common pitfalls and similar expressions

• Sentence end and before a noun
  • 不機嫌だった is a past expression meaning someone was in a bad mood.
  • 不機嫌な顔 means a displeased expression; な connects it to the noun.
• An uncertain cause
  • In the example, 寝不足のせいか means perhaps because of insufficient sleep. It does not establish that cause as certain.
• Mood and physical condition
  • 不機嫌 concerns a displeased mood, whereas 具合が悪い can describe poor health or condition. Being in a bad mood and feeling unwell are not the same.