It's by the Brussels-born (or not) 19th century eccentric Théophile Marzials, who was a librarian at the British Museum. His inclusion in the Oxford Dictionary of National Biography is all down to the poem's alleged unbeatable awfulosity. Read more about him here and here.
I dunno. I reckon I've read worse. I know for sure I've written worse, in my Rod McKuen days. Here's the offending pome:
A Tragedy by Theophile Marzials
Death!
Plop.
The barges down in the river flop.
Flop, plop,
Above, beneath.
From the slimy branches the grey drips drop...
To the oozy waters, that lounge and flop...
And my head shrieks - "Stop"
And my heart shrieks - "Die."...
Ugh! yet I knew - I knew
If a woman is false can a friend by true?
It was only a lie from beginning to end--
My Devil - My "friend."...
So what do I care,
And my head is empty as air -
I can do,
I can dare
(Plop, plop
The barges flop
Drip, drop.)
I can dare, I can dare!
And let myself all run away with my head
And stop.
Drop
Dead.
Plop, flop,
Plop.