That's crazy.
それはひどいな。
That will be funny.
It is a piece of cake.
〈何とも思わない〉 I don't care at all.
I don't care [give] a damn.
大袈裟だな。
You're overreacting.
This sounds interesting.
That won't work.
This is a pun.
It stands out from the others.
がっかりですね。
That's stretching the point.
That is serious.
Your views are absurd.