That's what she said...

I was asked what it was that I would take away from my visit to the US (when I finally leave that is). And after much thought it became evident that "that's what she said" has influenced me most and will forever be with me.
The idea, for those unfamiliar with this, is very similar to the fortune cookie deal where you read the fortune and add "in bed" to the ending. An excellent example of this is "They will definitely remember all you efforts"..."in bed".
As you can see it makes the fortune all that more funny.

So, a step up from that is "that's what she said" which implies there was once a female friend of yours who said whatever phrase had just been said.
Proceeding with examples:
1: Say you were climbing with some friends, trying to get to the top of a boulder problem. At some point one of your friends says "This is sooo f'ing hard!!!" Perfect opportunity for you to say "that's what she said".
The tone and volume of the voice is extremely important too. One shouldn't say it at the same volume as the phrase was said in, so as to make it seem like you are recalling a moment.
It should come out spontaneously, effortessly ("that's what she said").

Well, this morning, has I walk along the corridor leading to the door of my office, the cleaning lady steps out of the office and greets me:
-Good morning!
-Good morning!

-I just finished mopping the floor.
-Oh, that's ok.

-It is still a little wet.
-...(insert above phrase)