真失望 it's a bummer
(1) bummer “令人悲观或懊恼的景象，失望”
英语证明为a situation that is disappointing or annoying。
(2) it's a bummer “真失望”，美剧中很常用
大概不妨径直说一个单词bummer
例
It's a bummer.
真失望！
More than a bummer, Haley. This was really important to me, and you blew it.
岂止是失望，海莉。此次实行对我来说很要害，却被你弄砸了。《时髦家园》
失望 a wet blanket
(1) a wet blanket “失望的人，泼冷水的人；失望的事，焚琴煮鹤的情景”
英语证明为someone who ruins other people's fun。
(2) 用法根源为：爆发火警的功夫，不妨用湿绒毯盖到火上去熄灭；厥后扩充为在应酬场所失望的人、煞得意的人。
例
Come on, stop being such a wet blanket!
委派，别这么失望！
I'm sorry to be such a wet blanket, but I'm afraid I have to go home now.
不好道理，扫大师的兴了。然而，我真得还家啦。
妨害氛围 kill the mood
(1) mood 除去表白“情绪，情结”，也不妨表白“氛围，气氛”
(2) kill the mood “妨害氛围，失望”
(3) a mood killer “妨害氛围的人或实物”
(4) lighten the mood “活泼氛围”
例
I'm so sorry to kill the mood.
特殊对不起妨害氛围。
A: Are you kissing?
尔等在亲吻吗？
B: That's a bit of a mood killer.
你可真会妨害氛围。