I cannot have this conversation again.
I already told you how I feel about you going to Europe by yourself. I cannot have this conversation again.
We argued for a whole day about this. I cannot have this conversation again.
I don't want to talk about it.
Look, I don't want to talk about it. She's with somebody else now and I don't care.
Drop it/leave it
He obviously doesn't want to answer you so just drop it.
She already told you she doesn't like you. Let's leave it at that.
The matter is closed.
The board won't approve of the buyout. They'll vote against it this afternoon. The matter is closed.
There'll be no more discussion on it.
I told you what you need to do so either you do it or leave. There'll be no more discussion on it.
Your mom and I don't approve of you dropping out of school to become a musician and that's final.
I won't buy you X-Box. That's final.
You can't go to the bar tonight. That's final.