Green’s Dictionary of Slang

an insignificant person.

1942		J. Weidman cited in AS XVIII:1 (1943) 46: pish-er (noun) a Good Late American Colloquialism Denoting a Guy Who Gets Caught Between Two Other Guys, Usually With Muscles.
1963		A. Baron Lowlife (2001) 172: For that idiot, that little pisher, I was in trouble.
1986		S. King It (1987) 57: At least until the pisher knocks her up.
1996		H. Roth From Bondage 392: Pishkeh a little pisser.
1999		J. Ridley Everybody Smokes in Hell 144: I’m going to nail that little cocksucking pisher prick to the goddam Hollywood sign.
1999		P. Temple Black Tide (2012) [ebook] What do these pishers know about skill? Nothing.
2005		Mad mag. Apr. 34: Gag, you little pischer!