George Costanza: Anna told me that Elaine said I was one of the worst seeds she'd ever seen.
Jerry Seinfeld: Interesting. She doesn't care for you. Then a stern warning. Suddenly a phone call. Seems Elaine's made you the bad boy. And Anna digs the bad boy.
George: I'm the bad boy. I've never been the bad boy.
Jerry: You've been the bad employee, the bad son, the bad friend.
George: Yes. Yes. Yes.
Jerry: The bad fiancé, bad dinner guest, bad credit risk.
George: OK, the point is made.
Jerry: The bad date, the bad sport, the bad citizen. The bad tipper.
[Jerry and Elaine found out that the TV that they gave to Drake and his girlfriend was given to his girlfriend after they broke up.]
Jerry: We're not getting that TV back.
George: What do you mean? I mean you gave it to them, we get it back.
Elaine: The Drakette took it.
George: She can't take it. It's not hers, it's theirs. Once there's no theirs, there's no hers. It should be ours.
George: My name is George. I'm unemployed and I live with my parents.
The Suicide - S3-E15
Jerry: Let me ask you someting. If you named a kid "Rasputin", do you think it would have a negative effect on his life?
Jerry: You can't keep avoiding her.
George Costanza: Why not? If she can't find me, she can't break up with me.
Jerry: I'm not gay. Not that there's anything wrong with that.
George Costanza: It became very clear to me sitting out there today that every decision I've made in my entire life has been wrong. My life is the complete opposite of everything I want it to be. Every instinct I have, in every aspect of life, be it something to wear, something to eat - it's all been wrong.
Chosen answer: George does mention his brother in the episode "The Parking Space". They actually really never mention anything that contradicts the fact he had a brother though, it just isn't mentioned.