Green’s Dictionary of Slang

wisenheimer n.

also weisenheimer, wisenstein
[wise adj. (1) + Ger./Jewish sfx -heimer, usu. part of a surname]

1. a know-it-all, a self-appointed smart fellow.

[US]Ade Girl Proposition 72: The Original Gentleman Friend was a Wisenstein. As soon as he saw himself losing out, he began to lay deep and shifty Plans.
[US]S. Lewis Babbitt (1974) 228: The wisenheimers grab a look at a fellow’s nails when they want to tell if he’s a tinhorn or a real gent!
[US]W. Winchell On Broadway 23 Nov. [synd. col.] The wisenheimer laughed and took the wager.
[US]B. Schulberg Harder They Fall (1971) 208: He ain’t quite the weisenheimer he was when he came in from Two.
J.D. Salinger in Rawson Wicked Words (1989) 420: We were nervous [...] at the statistics on child pedants and academic wisenheimers who grow up into faculty-recreation-room savants .
[US]R. Dougherty Commissioner 44: These two wisenheimers wound up getting treated like hicks in a whorehouse.
[US]L. Rosten Dear ‘Herm’ 100: In case some wisenheimer in our midst throws Mr. Pulsifer [...] a slider.
[US]S. King Different Seasons (1995) 486: The cabbie gave a why-do-I-always-get-the-wisenheimers snort ... but he shut up.
[Can](con. 1920s) O.D. Brooks Legs 53: I was certain some wisenheimer had learned about our intended break and ratted.
[UK]J. Meades Fowler Family Business 84: Sullen Ben and the Wisenheimer Lennie.

2. attrib. use of sense 1.

[US]D. Hammett ‘Fly Paper’ Story Omnibus (1966) 52: He smiled that wisenheimer smile of his.