Having never seen one episode, I've never known where that came from. The commercial parts guy and I used to use it joking around all the time. Seinfeld's brand of humor just always rubbed me the wrong way. Never got into it.
I like it. It's an acquired taste, though. It couldn't be made today. It's way too offensive for all the thin skinned snowflakes out there now.
There's backstory, but not much plot. Four very flawed, dysfunctional friends and the ridiculous situations in which they behave badly.
I know you like baseball and movies. I don't know if you've seen JFK, but here's a parody. It's still funny.