you can use it, söyle alone is an imperative case "Tell" 

Example:

 1 -- Bir şey söylicem sana

 2 -- Söyle.

I will tell you somthing,

Tell, or Speak.

Bir şey söyliceğim sana.

^ : "Sana bir şey söyleyeceğim." Would be the grammarly true sentence.

And as alone it is imperative case too just like any other verb.

Thank you so much, KediNero.

Episode 10, 3:54:

http://www.fox.com.tr/Kiraz-Mevsimi/bolum/10

I´m curious if anyone has heard of Kiraz Mevsimi or watches it? It´s a silly show, but I like it.

Girl: Bir şey diyeceğim.

Guy: Söyle

He said söyle, and it sound perfect. But if he said bana söyle / söyle bana than it wouldnt be correct. Also he could say de instead of söyle, they are both correct 

Thankyou. Bana söyle in this situation would not be correct? because they are already talking?

If someone is not behaving nicely can I say fena gidiyorsun? Otherwise what would that mean and how would you say to someone you are not acting nicely?

yes, bana söyle is not correct in this situation.

i would say: 

ne bu saygısızlık?

ne bu tavır?

fena gidiyorsun=you are going bad

Thanks. I found another one: Kendine gel - behave yourself

But this must be an expression - literally is come yourself

yes you can also say like that if you think he don´t know what he is saying . Also if someone is drunk or he don´t feel good you can say that to him

Also:

Terbiyesizlik yapma 

Terbiyeli ol

Biraz saygılı ol

Saygısızlık etme

Çocukça davranma

Aptalca davranma

Gerizekalılık yapma

Nankörlük etme (you can say that to someone who don´t behave good, but you did many things for him)

2 more questions.

1. Sen gelmez oldun is a song. I saw the line translated somewhere as: you didn´t come. Confused with gelmez since this is he/she doesn´t come rather than you? Is this more like: You are the one who never came?

2. I think I heard büyükmüş said. What does that mean if anything? I thought it was said to mean "he has grown" but I may not have heard the word exactly.

maz/mez  Oldu  Form ;

With negative aorist tense [mAz] with oldu expresses the action,event ceased to happen.

        Verb stem + maz,mez + oldu + person

Sen gelmez oldun. ---> You stopped coming. [ You used to come but you stopped coming]

O artık bana selam vermez oldu ---> He/She stopped greeting [saying hello to] me.

Onlar bir süredir çay içmez oldular ---> They stopped drinking tea for a while.

Son zamanlarda birbirimizi görmez olduk ---> Lately , we, for some reason unable [stopped] to see eachother.