Wikipedia isn't much help, but a start on my linguistic quest
means something akin to "great" either realistically or sarcastically. Also spelled 'pissah'. This is just the word "pisser" with a Boston accent. Often combined with "wicked" to yield "wicked pissah".
From Issue of November 16, 2006 -- Page 3
The slang use of "wicked" to mean "excellent" (or as a positive intensifier, as in "wicked fast") is indeed native to New England, especially the Boston area, but it has spread widely into other areas of the US since it first became popular in the 1980s. Surprisingly, use of "wicked" in this ironic sense dates back at least to the 1920s, with the first occurrence in print found so far being in F. Scott Fitzgerald's "This Side of Paradise."