that was it

Yes, "that was it", said with emphasis on the word "it", conveys idiomatically the idea of some climactic point, good or bad, or moment of decision having been reached.

People say things like "I fell in love with Mary the moment I met her. We looked into each other's eyes and that was it". Or, "I took my new car back to the garage four times to have things fixed, but when a wheel fell off, well, that was it. No more!".

A similar idiom would be "that's all s/he wrote", meaning that there was no more to be said.

Thanks, these little idioms somehow can't find their way into dictionaries.

Theres gotta be a dictionary of idiomatic phrases because our culture couldnt get along without em. We run with phrases and use them intensely , then, all of a sudden, everyone stops using on because it has become trite. Then we rush off and adapt to another batch of phrases that occupy our speech for at least a year or more.
We have a strtigraphy of dead phrases that we use to "date" our communications.

They are often meant to be slightly humorous, ironic, or sarcastic.
Often , in classes, I get the idiomatic phrases and colloquialisms in papers from students and its quite amazing, the staying power that some of these phrases have. For me, the latest is one where the stdents accuse each other (and me) of having an "attitude", meaning that they feel they are being disrespected. Im always poking them to be more creative in their choices of words and I have a STAPLES buzzer that when you push it , says 'There, that was easy". Silly, I know, but Ive got a small war on idiomatic phrases being used by graduate students in science. Really honks my flivver

I can dig it man.

Of course. I have Ammer's dictionary, now available free of charge on Answers.com.

I can smell where you're comin' from . . .

DY-NO-MITE

It's out-o-sight, Dude . . .

Fully sick homey.

I googled "English idioms" and lo...

http://www.google.com/search?hl=en&q=English+idioms