Ross: Anyway, one thing lead to another, and… oh… before you know it, we were kissing. I mean,

how angry do you think Joey is gonna be?

Rachel: (now looking up at the ceiling) That is hard to say, Ross. That is hard to say.

Ross: You know, I gotta go find him. He’s gotta be here someplace.

Rachel: You would think!

Explanation:

before you know it   used to say that something happens very quickly and when you are not

expecting it :

You’ll be home before you know it.

قبل از اینکه فکرشو کنی، خونه خواهی بود.