In Swedish, the expression "det var droppen som fick bägaren att rinna över", directly translated to "the droplet that caused the beaker to overflow", is used to express that enough is enough. Is there a similar expression in English?
The straw that broke the camel’s back.
This write-up traces the saying’s history back to long ago, noting that Seneca once wrote in “On Despising Death” (Letter XXIV):
Counting even yesterday, all past time is lost time; the very day which we are now spending is shared between ourselves and death. It is not the last drop that empties the water-clock, but all that which previously has flowed out; similarly, the final hour when we cease to exist does not of itself bring death; it merely of itself completes the death-process.
And the online thesaurus seems to think that “match in the powder barrel” is a synonym for “the straw that broke the camel’s back”.
I just have to include my favorite expression, "It's always the last thing you did that got you in trouble" - it somehow always seems to be true. In your expression, it was adding that last drop that overflowed the beaker.
There is a perfectly elegant way to say it and it is known in the English lexicon. It does, however, suggests too much of something good, rather than bad:
His cup runneth over.
It's a Biblical excerpt . Used in the negative sense, it might make for a clever play on words, say, used for irony or a sarcastic comment. Context would matter. Example:
After her speeches on altruism and the disgrace of poverty, the head cheerleader's cup runneth over with catty comments about her family and her lifestyle.
This is the drop that filled the glass.
or else simply:
This was the last drop!
There are probably more (as @tchrist's answer shows).