When a verb is in its original form

[GoodTaste]

I am not sure why the girl used be rather than are:

(The context
Mr.A: Let's have a chat.
The girl: Only you be nice.

Did the girl mean "if only you will be nice to me"? I'm not sure whether the girl is a native English speaker. My intuition simply told me that she used be correctly.

My question is, does the grammar "you be" convey the future tense of the verb be if the grammar of "you be" is correct?

Another example is:

Winner take it all.

Does it refer to:

Winner (will) take it all?

Because in present tense, it should have been:

Winner takes it all.

 

[Skrej]

I am not sure why the girl used be rather than are:

(The context
Mr.A: Let's have a chat.
The girl: Only you be nice.

Did the girl mean "if only you will be nice to me"? I'm not sure whether the girl is a native English speaker. My intuition simply told me that she used be correctly. Possibly, but see below.

My question is, does the grammar "you be" convey the future tense of the verb be if the grammar of "you be" is correct?Not exactly - see below.

Another example is:

Winner take it all. The more common expression is "Winner take(s) all." It's a set expression.

Does it refer to:

Winner (will) take it all? Yes, but it's not a standard way to talk about the future, it's just referring to the future allocation of winnings. It just means that there's only one winner - no distribution of prizes between runner ups.

Because in present tense, it should have been:

The winner takes it all. Without an article, then it's just another variation of the above set expression.

The only way I can see 'Only you be nice' being grammatically acceptable is if she's using it an imperative. She's agreeing that they can talk, but giving him an warning and an imperative. She would probably pause after 'only'. "Only, you be nice."

In essence however, yes, she's agreeing that they can talk if he's nice.

Your second phrase is a set expression, so I wouldn't consider it a second example of the first phrase. They're referring to different contexts.

Of course, you could make a sentence like "The winner takes it all" - as in the ABBA song by the same name.

 

[Raymott]

Of course, that could also be a typo for "Only if you be nice." The 'be' question would remain.

And that brings up the question of the acceptability of:
Friend: Did you say you'd chat with him?
Girl: Yes, but I told him only if he bes nice."

 

[SoothingDave]

Looks like an imperative to me.