First, we were struggling to cope with the heavy workload on a seriously tight schedule, and then the very committee meeting we were working so hard for has been put off until next month. That was the only thing missing (that we needed)!
First of all, [Только этого не хватало!] is 100% "official" phase for that case.
I do not understand why you are not satisfied with that option.
It is contemporary, widely used, well known phrase.
Update
Only now in comments I've noticed, that you are interested not in translating [Il ne manquait plus que ça], but in translating [C'est le bouquet!].
Strange, that you have not put [C'est le bouquet!] to the title of your quesiton.
As I understand you are interested in territory of jargon.
It depends on the region of Russia.
But where I live, it is Urals, 2000 km east from Moscow.
For this case we have 3 options
1.
[Контрольный выстрел в голову.]
means a head shot which killer does from the gun to have 100% guaranty that the object is really killed.
Example.
On the exam day my alarm clock got broken and I overslaped, missed the breakfast. I got C on exam because I got the only question from a list of 80 questions which the have not studied. I've studied 79, but not this one. I got back home only to find out that my beloved cat had died today. [Контрольный выстрел в голову.]
2.
[Короче, приехали...] [В общем, приехали...]
means [we have come] or [we have finally arrived to place...]
On the exam day my alarm clock got broken and I overslaped, missed the breakfast. I got C on exam because I got the only question from a list of 80 questions which the have not studied. I've studied 79, but not this one. I got back home only to find out that my beloved cat had died today. [Короче, приехали...]
3.
[Короче, тушите свечи...] [В общем, тушите свечи...]
means, [put out candles]
On the exam day my alarm clock got broken and I overslaped, missed the breakfast. I got C on exam because I got the only question from a list of 80 questions which the have not studied. I've studied 79, but not this one. I got back home only to find out that my beloved cat had died today. [В общем, тушите свечи...]
Bonus track
On the exam day my alarm clock got broken and I overslaped, missed the breakfast. I got C on exam because I got the only question from a list of 80 questions which the have not studied. I've studied 79, but not this one. I got back home only to find out that my beloved cat had died today. [Одним словом, денёк типа зашибись...]