In your dreams:

在你夢里 ×

做夢去吧 √

例句：

In your dreams! There's no way you can make it.

做夢去吧！你不可能會成功的。

我敢說、我敢打賭:

① I bet

② I'll say

例句：

① I bet he'll spend all his money in a few days because the money is burning a hole in his pocket.  

我敢說，不出數(shù)天他便會把錢花光，因為他是個留不住錢的人。

② I'll say you made it all up.  

我就說是你胡說八道。