Although today we're looking at an N1 grammar point, which means you won't hear it terribly often in conversation, it's still a pretty awesome piece of language:

JLPT N1：～たら最後

This phrase equates to something like, "if... that'll be the end of it" in English.

Let's dive right into an example:

彼女を怒らせたら最後、１ヶ月は目も合わせてくれない。
かのじょ　を　おこらせたらさいご、　いっかげつ　は　め　も　あわせて　くれない。
If I make her mad, that's the end of it. She won't even look at me for a month.
Literally: "she + を + if (I) made (her) angry + end / last / final, + one month('s time) + は + even make eye contact (and) + won't give (me)."

Note: 目を合わせる (めをあわせる), literally, "eye + を + match / join together," means "to make eye contact." Note that we changed を to も to emphasize that she won't even do this.

So in the first half of our sentence, we have an action. In this case it's, "If I make her mad."

Then in the second half of the sentence, we have some unfortunate consequence. In this case it's, "She won't even look at me for a month."

怒らせたら ／ If I make her mad
最後 ／ that's the end of it
目も合わせてくれない ／ she won't even look at me

This ～たら ending is used for if-statements, and if you don't know it, then you shouldn't really be looking at N1 grammar just yet. Don't worry; we'll eventually have studied six N4 lessons using ～たら！

最後 (さいご // end; last; conclusion; final), also, is an extremely common word, which you probably should learn before even taking N5.

---

Tangent!

While you could probably get away with saying the above sentence, I can't help but teach a considerably more popular way to express the idea that angering one's girlfriend or wife can result in grave repercussions:

彼女を怒らせたらもう終わりだ。
かのじょ　を　おこらせたら　もう　おわり　だ。
Once I make her mad, it's all over.
Literally: "she + を + if (I) made (her) angry + already + the end + だ."

---

Let's get back to our N1 goodness... by looking at another example!

そのサイトに登録したら最後、大量の迷惑メールが毎日届くようになりますよ。
その　サイト　に　とうろく　したらさいご、　たいりょう　の　
めいわくメール　が　まいにち　とどく　ように　なります　よ。
Once you register on that site, that's the end of it. You'll start getting tons of spam mail every day.
Literally: "that + site + に + registration + if did + end / last / final, + large quantity + の + spam (=annoyance + email) + が + every day + be delivered + ように + become + よ."

---

Construction

Now, you maybe be thinking, forming these sentences is cake. All I gotta do is take a ～たら verb and add 最後.

Yes, that's true.

But you can also take a past tense verb and then add が最後 to make your sentences even less colloquial:

V たら ＋ 最後
V た ＋ が ＋ 最後

Example:

彼に好きな歌手を聞いたが最後、クリス・ブラウンの素晴らしさを長々と聞かされる。
かれ　に　すき　な　かしゅ　を　きいたがさいご、　クリス・ブラウン　の　すばらしさ　を　ながながと　きかされる。
If you ask him what singer he likes, that's the end of it. You'll have to listen to him describe at length the magnificence of Chris Brown.
Literally: "he + に + liked + singer + を + asked + が + end / last / final, + Chris Brown + の + magnificence + を + very long / drawn out + と + be informed about."

---

And our final example:

一度カキにあたったが最後、もう二度と食べたくなくなる。
いちど　カキ　に　あたったがさいご、　もう　にどと　たべたくなくなる。
Once you get food poisoning from oysters, you won't be able to eat them ever again.
Literally: "one time + oysters + に + got sick from* + が + end / last / final, + further + two times + と + not want to eat + become."

Note: We have あたった, which is the past tense of あたる, which has like a million uses in Japanese. The original meaning is something like, "to hit on," like how you "hit a jackpot." Or, as in this case, it can mean to have your stomach "hit" by some food in an altogether unpleasant manner. ^^

---

Now, did you really go through all of those translations above?

If so, how you do feel about reading those sentences again with no kana or translations?!

彼女を怒らせたら最後、
１ヶ月は目も合わせてくれない。

そのサイトに登録したら最後、
大量の迷惑メールが毎日届くようになりますよ。

彼に好きな歌手を聞いたが最後、
クリス・ブラウンの素晴らしさを長々と聞かされる。

一度カキにあたったが最後、
もう二度と食べたくなくなる。

Happy studies, yo.