Trivia: The Cat Juggler, in the film, was Steve Martin. (01:12:40 - 01:13:30)
Trivia: "Cat Juggling" was a bit in Steve Martin's stand-up acts in the late 70's.
Trivia: Director Rob Reiner has a cameo as the truck driver who takes Navin to the end of the fence.
Answer: Navin self-applies the "Jerk" epithet early in the film, using it not in the sense of someone obnoxious or mean (as it is used in most cases), but in the sense of a stupid person. He's saying he blames himself and his lack of intelligence (though, as you say, it is usually simple naïveté) for ending up where he is (broke, homeless).