This beauty is a combo of “at the end of my rope” and “the last straw”, both meaning to be at the end of one’s endurance. Straws and ropes are similar in shape and even texture, adding to the mental confusion. A tip of the toque to Paula Fow for sending this congruent conflation to me.
This is a mash up of “the last straw” and “another nail in the coffin” (both meaning the final problem that will lead to a collapse or end). I saw this one on yardflex.com, which is a website about Jamaican issues:
“All respect to Trinidad, but they own more of the country’s assets than we do, selling them Air Jamaica will now be the last straw in the coffin.”
I AM the malaphor king, mon.