Well, let's do it then. (And we can go with that.)
I have no objection. 我不反对
I can't do anything about it. 实在无能为力
That's also a valid option. 这样也可以
Another time, then. 下回吧
No thanks, I've had my fill. 感谢了，已经足够了（还要一块蛋糕吗？）
This is really noteworthy, but... 虽然值得注意，但...
I'm not in the mood for it right now. 现在没什么兴趣
I'm sorry, I have a lot to do. 抱歉，我现在很忙
That's not happening! 不行
Absolutely not. 绝对不行
I cannot do that. 办不到
I'm sorry, swimming isn't my thing. 对不起，我不太喜欢游泳
Smoking is prohibited here. 禁止吸烟
Please don't be so loud. 请勿喧哗
I already have plans. 我另有安排了
No, I can't come with you. 哎呀我就不去了
Ah... 这个...
It's average, to say the least. 只能说一般般
Yes, possibly. 也许吧
I need to think about it. 我需要考虑考虑
That's a secret. 这是秘密哦
How should I put it... 我该怎么说
One could also say... 也可以说
