down-in-the-mouth

角田光代の "The Eighth Day" (原題　八日目の蝉)を読んでいます。
"Sorry, but I'm going for a drink with my friend here, so tonight's off," I told Kishida, dismissing him with a nod and hurrying on past, leaving him standing in the alley. Chigusa stared back at him as she walked beside me, one hand resting on the handlebars. I suppressed a desire to look over my shoulder.
"Rika-chan, is that guy back there your boyfriend? He's looks a bit down-in-the-mouth," she said once we were out of the alley, turning around for one more look.
Kiwakoとデートしようと思っていたKishidaはChigusaのお陰でそれだ駄目になったので嬉しいわけがありません。ということは "down-in-the-mouth" はその反対の意味ですね。辞書で確認します。
・Oxford English Dictionary: (of a person or their expression) unhappy; dejected.: It seems that City stockbrokers are a little down in the mouth.

・Collins Dictionary: unhappy or depressed: As for George, I hear he's rather down in the mouth.

・Wiktionary: Sad or discouraged, especially as indicated by one's facial appearance.: Don't get down in the mouth about business in this country. There is going to be a lot of money spent here.