I mean, clearly you're still sharp as a tack.

虽说你依然非常厉害。

You could have several beers at lunch and still be sharp as a tack during the company meeting at 2 PM.

比如你可以在午餐喝几杯啤酒，然后精神如常的在下午两点参加公司会议。

Right now you're sharp as a tack.

现在你还很敏捷。

Yeah, she does seem sharp as a tack.

是啊 她的确突然容光焕发了。

So if you're sharp as a tack, it means you're very smart.

所以，如果你像大头钉一样敏锐， 那就意味着你非常聪明。