Someone who is actually NOT handicapped or retarded, but through his deliberate ineptitude and lameness gives off the impression that he is BOTH handicapped AND retarded.
Jack: Dude, I think I'll vote for Hillary Clinton for President.
John: Dude, you're a handitard.
A defining characteristic of those priveldged people who get the ride the short bus, get preferential customer parking or otherwise given "special" treatment. A slang of handicap and retard.