“Leftard” (left + retard) is an epithet used by some on the political right against the political left. “Leftard” has been cited in print since August 2004.
 
Similar terms include “sheeptard” (since March 1999), “Republitard” (since April 2002), “rightard” (since January 2003), “patriotard” (since April 2003), “Demotard” (since July 2003), “libtard” (since July 2004), “libertard” (since February 2004), “GOP tard”/“GOPtard” (since July 2004), “wingtard” (since October 2004), “neotard” (since May 2002) “conservatard” (since November 2005),  “truthtard” (since October 2006), “ecotard” (since July 2007), “climatard” (since December 2008), “teatard” (since March 2009), “crumbtard” (since May 2011) and “occutard” (since October 2011).
     
 
Urban Dictionary
leftard
Someone who is so far left-wing in ideology, that they make others believe that the person must be mentally handicapped - read: Retarded, to have such opinions.
person 1: Did you hear Amy talking about how 9-11 was an inside job? That Bush actually knew about it and that Cheney actually planned it.
person 2: Don’t listen to her, she is a Leftard.
by DK668 Nov 13, 2007
   
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From: “John De Gennaro”
Date: Tue, 31 Aug 2004 19:31:02 GMT
Local: Tues, Aug 31 2004 1:31 pm
Subject: More of that “adult” behavior that the leftards love to display to the world
   
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From: Jim Alder

Date: Mon, 20 Sep 2004 16:34:12 -0000
Local: Mon, Sep 20 2004 10:34 am
Subject: ‘Leftard’ Heydope’s Finger in his nose.