"Pisseroo" or "Pisserroo" is a variant of "pisser", a slang term for something very bad. "Pisser" is defined by Merriam-Webster as "one that is inferior, difficult, or unpleasant" and by Cambridge as "something that is of very bad quality".
"Pisseroo" is a humorous development of "pisser", using the "-eroo" suffix which Dictionary.com defines (based on the Random House Unabridged Dictionary, 2022) as:
a suffix that creates familiar, usually jocular variations of semantically more neutral nouns; normally added to monosyllabic bases, or merged with bases ending in -er: flopperoo; smackeroo; switcheroo.
"Pisseroo" evidently follows the same logic.
An example from A Hall of Mirrors, Robert Stone, 1997, a novel by a New York-born novelist set in New Orleans.
"Boy," he said. "This is a pisser. This is a pisseroo, Reinhardt. I wish I had your job today."
The Cambridge Dictionary definition cited above also notes that "pisser" can be used ironically for something good, so it's possible you'll see "pisseroo" in a similarly ironic sense, but generally it means something bad.