Do you guys know the word 後悔 (こうかい； koukai)? Or the verb phrase 後悔する？ 後悔 is "regret" and as always, adding する verbs it into "to regret." So what about "regrettable?"
後悔的 doesn't really get used very commonly, so if you want to say that something was regrettable, like Brett's decision to sing Mariah Carey's "Fantasy" at Karaoke, you could use the first half of today's yo-ji、遺憾（な）to do the trick: ブレットさんの音域が狭すぎて、極めて遺憾な演奏でありました。
So, with 遺憾 as "regrettable" and 千万 stepping up to represent an extremely large quantity, we've got a yo-ji that means:
1. HIGHLY regrettable.
It's worth noting that while all of these translations could be applied equally to Brett's singing, you can use 遺憾千万 in lots of other situations as well. The Yoji Databank has a good example with: 「よかれと思い、君に忠告したつもりだったが、逆に恨みを買うとは遺憾千万だ。」 I particularly like the phrase 「よかれと思う: to have good intentions; to mean well.」
Sadly, I have a lot of memories that I look back on as 遺憾千万. Most recently, I was filling out an application at a job interview, and thanks to a combination of nerves and a really crappy clipboard, my 字 were coming out all 汚い. So to help correct that, I took a magazine off of the waiting room table, slipped it in between the clipboard and the paper, and finished filling it out. Unfortunately, when I was all done, I forgot to take it back out and 雑誌がはさんだまま返しました。The girl who was interviewing me noticed it, and noticed that everywhere I had pressed down hard in the attempt to write clearly, the 字のなぞりは雑誌の表紙に残っていました。
She was not pleased.
I like to think of this 四字熟語 as it compares to 言語道断.
Note though, that 遺憾千万 carries a connotation of うらみ (resentment) on someone's part.
Today's example will be a simple one, and hopefully easy for you to use.
It's beyond regrettable that you can't understand that.