Actually, he based on a real person, and is more realistic then 80% of the sitcom characters I have seen.
Remember his pickup line from the “do the opposite” episode:
George Costanza: Hi, my name is George, I’m unemployed and I live with my parents.
More classic George lines:
George Costanza: Do you ever get down on your knees and thank God you know me and have access to my dementia?
George Costanza: The sea was angry that day, my friends. Like an old man trying to send back soup in a deli.
Jerry: You wanna see an idiot? Here. I am an idiot. Elaine just gave me a chance to back out and I didn’t take it. Now, she’s gonna be my neighbor.
George Costanza: You? You are no match for me. I just passed up a lifetime of guilt-free sex and free sporting events. You are no competition, for I am “Costanza- Lord of the Idiots”!
George Costanza: When she threw that toupee out the window, it was the best thing that ever happened to me. I feel like my old self again. Neurotic, paranoid, totally inadequate, completely insecure. It’s a pleasure.
Gary Fogel: [to George] I’ve been living a lie.
George Costanza: You’ve been living a lie? I’ve been living like twenty!
George Costanza: George is gettin’ very angry!
[George wants the nickname “T-Bone”]
George Costanza: Ladies and gentlemen, I have an announcement. From now on, I will be known as…
Kruger: Koko the Monkey.
Jerry: Why didn’t you tell her your code?
George Costanza: I can’t give away my code to her.
Jerry: George, you’re gonna marry this woman… probably.
George Costanza: No way. The bank clearly says “Don’t give away your code to anyone”.
Jerry: So, you’re taking relationship advice from “Chemical Bank” now?
George Costanza: Why does it always have to be “us”? Why can’t there be a little “me”? Is that so selfish?
Jerry: Actually, that’s the definition of selfish.
and:
George Costanza: So I’m the bad boy. I’ve never been the bad boy before.
Jerry: Why not? You’ve been the bad employee, the bad son, the bad friend…
George Costanza: Yes, yes, yes…
Jerry: The bad fiancé, the bad dinner guest, the bad credit risk…
George Costanza: OK, the point is made.
Jerry: The bad date, the bad sport, the bad citizen…
[George leaves]
Jerry: The bad tipper!