Bad Mood
Grumpy, Sullen
noun, な adjective
Remember how 機嫌 means mood? Well when you add not it becomes a bad mood. It's so bad it's like you have no mood at all.
ふきげん
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
コウイチがつまらない冗談を飛ばすと、ビエトは不機嫌になる。
When Koichi cracks a lame joke, Viet gets in a bad mood.
そんな不機嫌そうな顔しないでさ。楽しもうよ！
Hey, don't make such a sullen face. Let's have fun!
昨日遅く寝たのに朝五時に起きなくてはいけなかったので、今日は一日中不機嫌だった。
I went to bed late last night and had to get up at five in the morning, so I was grumpy all day today.