I was going to mention it, but it slipped my mind.

我正要说到它，可是想不起来了。

Sorry, it slipped my mind.

对不起，我不小心给忘了。

I was just so busy it slipped my mind.

但是我太忙了，所以忘记了。

It slipped my mind.

从大脑里溜走了。

I did mean to call her, but it slipped my mind.

我确实想打电话给她，但不留神我忘记了。

It slipped my mind that I was visiting him today.

我忘了，我今天去拜访他。

It slipped my mind that I had to turn in my homework by ten.

我忘记了我必须在十点前就交作业。

Oh right, it slipped my mind. Why do you celebrate two New Years?

喔，对了，我都忘了。你们为什么要庆祝两个新年啊？

I meant to tell you your girl friend had called, but it slipped my mind.

我本想告诉你，你的女朋友来电话了，但是我把这事给忘记了。这下你会用了吧！

I meant to tell you your girl friend had called, but it slipped my mind.

[解释]蟩忘记了。没记住。我本想告诉你，你的女朋友来电话了，但是我把这事给忘记了。

I meant to call you when I got to Beijing but I was so busy it slipped my mind.

我本来是打算到北京就给你打电话的，但是我太忙了，所以就忘了。

I'm sorry I forgot your birthday. It must have slipped my mind.

对不起我不记得是你生日，肯定是我忘记了。

I was going to invite you to the party but it must have slipped my mind. I'm really sorry.

我本想邀请你来参加聚会的，但我肯定是忘了。我非常抱歉。

I'm sorry I didn't make to your party. It just slipped my mind as I had too much work to do.

很抱歉我没能去成你的派对。有太多的事儿要做，我给忘记了。

Oh dear! It had slipped my mind that the Banks were closed today.

亲爱的，我忘记了今天银行是不上班的。

I meant to mail the letter, but it entirely slipped my mind.

我本来准备发这封信的，却完全给忘掉了。

I can't think of anything at the moment, but I know there is something important I have to do today. It just slipped my mind!

一下子我也想不起来，我只知道今天确实有要事要办，我都给忘得一干二净了！

I got in a daze and it completely slipped my mind.

我一着急就怎么想也想不起来了。

I'm sorry I didn't tell you. It completely slipped my mind.

抱歉，我没有告诉你。我全给忘了。

Oh, I'm sorry. It completely slipped my mind.

噢，很抱歉。我完全忘了。

I was going to invite you to the party but it must have slipped my mind.

我本想邀请你来参加聚会的，但我肯定是忘了。

I'm sorry I forgot your birthday; it completely slipped my mind.

我很抱歉忘了你的生日，我完全不记得了。

It nearly slipped my mind that I've promised to take you to Shanghai.

我差一点儿忘了我曾答应过要带你去上海的。