…Snapple?
It’s European!.
“…she’s a 'two-face.’”
"Like the Batman villain? "
"If that helps you… "
“He’s a bad breaker-upper”
Helllooooooooooooooo…la la la!
I love that “Giddy-up” thing that Kramer does. Sometimes when my wife asks me if I feel like going out to dinner, or whatever, that’s what I say.
nonvite/unvitation
I thought it was only one suggestion per post? Some have posted multiple suggestions.
"I invented ‘It’s not you, it’s me’ ".
“Not on my watch, buddy”.
“The sea was angry that day, my friends.”
The coffee table book that turns into a coffee table.
“Get outta here!” (Elaine’s happy cry, accompanied by hitting someone hard on the chest).
“Dumper / dumpee”.
Why thank you!
I answer the phone this way. 
Remind me, please… what’s the story behind this one again?
It was the episode where dentist Tim Watley converted to Judiasm, which Jerry suspected was done only so he could tell Jewish jokes. Jerry proceeded to tell dentist jokes to other people, and it eventually got back to Tim. I think it was Kramer who used the phrase “anti-dentite” to describe Jerry’s condition first.
Jerry thinks his dentist converted to Judaism just for the Jewish jokes; he’s later accused of hating dentists.
Bosco.
[Jerry]
Alrighttt
[/Jerry]
Kramer: “I’m out!” The best delivery of two words in sitcom history.
Elaine: He took it out! (The beginning of my favorite Seinfeld conversation)
I doubt this counts but “coquettish haberdasher” has got to be one of the most amusing phrases ever spoken.
Father Whatley: And this offends you as a Jew?
Seinfeld: No, if offends me as a comedian.
Thanks, everybody - I’d forgotten that one.
That chimp’s all right.
I know the OP specified one per, but since people are posting multiples, I’m going to mention “Shiksa Appeal”, from the “Serenity Now” episode where a number of Jewish characters display attraction to Elaine Benes; George Costanza then explains this as a response to her “shiksa appeal.”