I don't think that's a good idea.

I don't think that's a good idea. それはやめたほうがいいよ

​I was going to ask the boss for some time off....
上司に休みを取れないか聞いてみようと思ってたんだけど....

​I don't think that's a good idea. He'll probably get angry.
​それはやめた方がいいと思うよ。多分怒られると思う。