Hello all,
Thnaks for your ongoing help in this forum.

I have a simple question regarding using past verbs to indicate future events.

Here is my example below (Taken from "The Boyfriend" episode - seinfeld)

George:I had a great time tonight, Carrie.

George:And I will call you as soon as I get home.
Carrie:Don't bother.
George:Bother? What kind of bother?
Carrie:I would prefer it if you didn't.

Why using 'didn't' in here? "I would prefer it if you didn't"?
is this would also be correct? "I would prefer it if you won't"?

Thanks a lot for all of you.

In an if-clause, the past tense form usually indicates hypothetical present or future time. These usually occur together with clauses that have would or could. Often, as in this case, this combination is used to weaken the statement, which makes it more polite.

I would prefer it if you didn't. (I prefer that you do not, said more politely.)

I would prefer it if you won't is not grammatically correct, even though you may feel that it is the real meaning.

So it's a lot about politeness, I see.

Thanks CalifJim!