It's no fun at all. I hate it. 这没一点儿意思,我讨厌它。
C'mon. Don't be a party pooper! 哎呀,你别扫兴嘛! You're such a sourball. 你太乖癖。
You're a real downer. 你真败人雅兴。 You're being a wet blanket. 你这样子等于在泼冷水。
Don't be a sourpuss. 别闹别扭了。