いいわけないだろ -- I'm not sure how to translate it properly

Question

I came across the phrase which I wrote in the title while reading a manga and I don't get it very well. At first I thought it was actually 言い訳 and the author didn't want to use kanji but after reading a few examples when I searched sentences, it's actually 良いわけない, so it would roughly translate as "That's no good"? Let me give a little bit of the context.
It's about two teenage boys and they have magic powers. Let's call them A and B. Each boy can summon a magical weapon. A is a better magic user and can wield his weapon very well while B is less trained, but at least he can summon his weapon. B asks A to train him.
*B summons/takes out his magical weapon and A says the following:

これ実家で保管してるやつでしょ？持ち出しちゃってよかったの？ (Is he saying "This the thing that is kept in your family, right? Isn't great that you can bring it out?")

I know it's a very rough translation...And now B replies with:

いいわけないだろ。早く使い方教えろよ。

So, I get the last part ("Hurry up and teach me how to use it!'), but the first one, I feel like he wanted to say "this isn't good" or even 'good enough'. It's just this small part that I need to know to understand something in regards to their powers.
Can someone help me out, please?

Answer 1

So glad you have provided enough context. Look carefully the two parts in bold below because 「いい」 responds to 「よかった」.

A: 「これ実家{じっか}で保管{ほかん}してるやつでしょ？持{も}ち出{だ}しちゃってよかったの？」

B: 「いいわけないだろ。早{はや}く使{つか}い方教{かたおし}えろよ。」

Understanding A's last sentence would be the prerequisite to understanding B's first.

In 「いいわけないだろう」, 「わけ」 means "reason", "grounds", etc. You use this phrase when responding negatively (and firmly) to a statement or question that talks about whether something is good or not. Please remember that we use this phrase very often.

Thus, 「いいわけない」 means 「持ち出していいわけない」 here.

Literally,

A: "This is the one that's kept at your parents' place, isn't it? Was it OK to take it out?"

B: "There is no good reason (for doing that). Hurry up and tell me how to use it!"

To translate B's first sentence more naturally, I would use:

"Definitely not!", "No way!", "Impossible!", etc.