Fonzie doesn't want to be Arnold's best man because of the Fonzarelli Curse. Richie says to Potsie and Ralph, "I haven't seen Fonzie this upset since Paula Petralunga became a nun." Apparently, Paula Petralunga didn't like being a nun because she is mentioned several times in the episode "The Duel" which aired during the sixth season. Also, we actually see Paula Petralunga in the episode "Going Steady" during season 10.
Fonzie: (referring to Marion) I think I'm gonna have to hit her!
Howard: No, you're not gonna hit my wife!
Fonzie: Oh, yeah? Well, then I'm gonna hit you!
Richie: You can't hit my dad!
Fonzie: All right! I'll hit you!
Howard: You can't hit my son.
Fonzie: Well, I gotta hit somebody. You know where Potsie is?!
Howard: Look, Fonzie...
Fonzie: All right, all right, I know, I'm going. I'm going. But I'm not going because I just got yelled at, and I'm not going because she thinks she's right and I'm wrong. I'm going because I'm a sweetheart of a guy!
Arnold: I'm getting married. I can't believe it. You know who made it all possible?
Arnold: The Fonz.
Fonzie: Hey, don't blame me for your problems.
(Fonzie refuses to wear a kimono.)
Fonzie: The Fonz don't dabble in female attire.
Richie: Well, Fonz, this isn't a dress.
Fonzie: Hey, let me put an end to this discourse right now, huh? One question: does it have a fly?
Fonzie: I rest my case.
Howard: How are you doing, Arnold? You got the jitters?
Arnold: No, no, we took a blood test. We're fine.
Fonzie: The only shot that those two people have is if I stay out of it. The Fonzarelli Curse cannot be broken. It's ridiculous to try. That's it, that's all, and that's goodbye.
Marion: Fonzie, sit on it!
Joanie: Everybody duck!
Richard Lee Sung is credited as "Richard Lee-Sung."