Thank you @GregoryP, a great appreciation to you, your comments helped me a lot.

Sometimes my mind jumps a lot, and you haven't seen the chat content, maybe that's why it makes you feel confused somewhere in the essay.

Let's discuss the guy's logic here, and I think it's not only about the use of informal words.

(Background:the indian guy's English is even poorer than I......We chatted by typing)
Firstly he asked my age and name, he thought my avatar looks as 13~14 years old.
And he said I have a beautiful face and charming lips.........
and he said he like me, and he ask me like him or not..........

Then I asked his age and gender, and he want to continue chat in a hurry......

We chatted for about one hour or more, and nothing else he could say except for saying my beauty.

I said to him twice that " I don't like the word sweet-heart you say, because I don't even know who you are" and he said"but I like that word, sweetheart, why don't like it? if you don't like, I'll never say it again, then can we continue chating？"

I feel a litte fidgety because it's a waste of time to chat for some un-meaningful contents, and he seem to tried to haunt the chat round about me. For example the last night when I was busy, he asked every half an hour"are you finish working" and I answered "it is 0:00am I'll sleep soon can we talk next time",and he asked"when we can talk next time" I thought I've got to be crazy.

I said "that is you ask me add you as a friend on QQ. I'm busy now, you can make a theme, ask me and I will answer you." and he said" I have no theme. 

Then he asked"could we make a voice chat" , now I was really angry, I said" I've told you it's over 0:00 already, how could you try to force me to disturb my roommates!!!!!"

Then he finished chat with a breaking heart....

That's the whole thing. I know that's a ludicrous story..

I don't think I can not tell the difference between informal word and improper purpose！！！！！

that's weird if someone's homepage is blank with none essay and twitter but he has followed nearly 200 people and nearly 200 people folowed him!!!!

Don't say "sweetheart" when u meet a Chinese girl online for the first time.

Don't say "I like you" when you meet a Chinese girl online for the first time.
当你第一次在网上遇到一个中国女孩时，别对她说“我喜欢你”。

She will probably perhaps <em>(可能 perhaps or probably?)</em> ask <em>(or 'She might ask...')</em> "so what exactly is it you like about me u like me about what?"
她可能会问：“那么你喜欢我什么？“

Maybe you've just seen her photos, and known her nickname and age.
也许你只是刚刚看了她的照片，刚刚知道了她的昵称和年龄。

but why how can you dare call her "sweetheart"？
但你为什么敢叫她“甜心”？

You know nothing about her，she is no-one of to you.
你根本不了解她，她也不是你的任何人。

She is just a stranger of everyone including you.  As far as anyone, including you, is concerned, she is just a stranger.
对于任何人而言，她只是一个陌生人，包括你。

Maybe you can share each other with different cultures with each other, and you can help each other with study problems,
也许你们可以分享不同的文化，可以相互帮助以解决学习问题。

but never try to find a intimate relationship on the internet.
但永远别试图在网上寻找一段亲密关系。

People all over the world have different kinds of daily business to attend to hang on.
全世界的人们每天都有各种不同的事情要去应对，

Most people just only believe what they see or what they can touch,
大部分的人们只相信他们能够看见或能够触摸的东西。

so what you do want me to see, behind your unreal online chatting content?
所以你想让我从那些虚幻的在线聊天内容背后看出什么？

Maybe you think that I'm a bad-tempered girl, but I want to tell you:
也许你认为我是个坏脾气的女孩，但我想告诉你

When you are the one who think all the young girls are stupid, you're the real stupid guy indeed.
当你认为所有的年轻女孩都是傻子的时候，你自己就是那个傻子.

<em>haha - 'sweetheart' 'dear' 'sweetie' 'honey' are all condescending and patronising!!! Stop anyone who says it unless they are very close to you</em>

Just had a quick look at you notebook and decided to make a few suggestions! 

Don't say "sweet heart" when you meet a Chinese girl online for the first time.

Don't say "I like you" when you meet a Chinese girl online for the first time.
当你第一次在网上遇到一个中国女孩时，别对她说“我喜欢你”。

She will probably ask" so u like me about what?" ask: “so what do you like about me?”
可能 = possibly 40%-60% chance
很有可能 = probably 65+% chance
她可能会问：“那么你喜欢我什么？“

Maybe you've just seen her photos, and known her nickname and age.
也许你只是刚刚看了她的照片，刚刚知道了她的昵称和年龄。

but why do you dare to call her your "sweet heart"？ (这个更自然)
但你为什么敢叫她“甜心”？

You know nothing about her，she is no-one of to you.
你根本不了解她，她也不是你的任何人。
任何人 is normally translated as anyone so you could rephrase it as
‘She isn’t anyone important to you’

She is just a stranger to everyone, including you.
对于任何人而言，她只是一个陌生人，包括你。

Maybe you can share each other with different culture, you can help each other with study problem,
也许你们可以分享不同的文化，可以相互帮助以解决学习问题。
Maybe you can share your different cultures with each other; you can help each other with your studies.

but never try to find an intimate relationship on the internet.
但永远别试图在网上寻找一段亲密关系。

People all over the world have different kinds of daily business to hang on.
全世界的人们每天都有各种不同的事情要去应对，

Everyday (每天) people have all kinds of (各种不同) of situations (事情) to deal with （应对 is normally translated as response but that is not natural in this sentence）

Most people just believe what they see or what they can touch,
大部分的人们只相信他们能够看见或能够触摸的东西。

so what you want me to see, behind your unreal online chatter?
所以你想让我从那些虚幻的在线聊天内容背后看出什么？

Maybe you think that I'm a bad-tempered girl, but I want to tell you:
也许你认为我是个坏脾气的女孩，但我想告诉你

When you are the one who think all the young girls are stupid, you're the one who’s stupid.
当你认为所有的年轻女孩都是傻子的时候，你自己就是那个傻子.