X Men Origins- Wolverine 
Wolverine : This does not change anything. I am done with you. 
Prompt reply by Sabertooth: We are brothers, we are never done with each other. 
And before the fight with the strongest mutant Sabretooth said to Wolverine “Nobody has the right to kill you, except me.” 

Brothers of Destruction (WWE attitude era) Kane and Undertaker would rip each other apart but together they would rip everyone else apart. 

The fact of the matter is sibling likes to kill each other, peel of the skin, rip off the nails, they loathe each other feel angry, disgusted with each other, but the license to insult the other one must always stay with themselves. They are fierce when they fight each other and they get more fierce if anyone else harm or hurt their sibling. 

Best part of your childhood and teenage, when you want privacy for some weird adventure, usually gets ruined by your sibling. 

If you are fond of writing diary you can be sure that, your not so cute brother or sister will be totally reading that. Then you come up with the plan of writing abuses in some of the pages of the diary like “Idiot! Its none of your business to read my stuff..” So in the process you both keep on planning some unusual way to disturb each other. You get disgusted, with each other. Jealous, probably kill each other a million time in dreams with 3D background effects, but in the end you love each other so very much. 
Present generation kids might consider putting up their siblings in OLX or Quikr. 

You really feel pissed witnessing the stupidity level of your sibling. Feel irritated by their inability to stay quiet even for a fraction of a second. If your sibling is younger to you, you will have to inevitably deal with they trying to copy you. You feel irritated, but you are not left with much option. But at the end of the day when, your sibling knows the biography of Bruce Lee, have watched Rocky series with you, recognises Viv Richards, or George Best, even being a girl which the boys from her class would fail to recognise, there will be a sense of pride in you. Or when your sister would dislike Twilight contradictory to all other girls of her age and would agree with you that, Voldemort was forced to Kill Cedric only after watching Twilight, you surely know that you have managed to teach the kid well. 

Also when your sibling knows the story of Lord of the Rings, Pirates of Caribbean, Rocky Rambo Series which even most of your male friends don’t know about, when you will see that both of your choices and likings are so similar, it will give you enormous liking to acknowledge that you have successfully cloned yourself into another human. 

But to achieve these, you will have to go through ages of torture, blackmailing and irritation. Not to mention all those advices about dealing with girls, but eventually your sister will bail you out in some relationship issues. There would be blackmailing sessions occasionally and you have to compromise on something so that your deepest, darkest secret don’t reach mom. 

Though at times you can have revenge by mentioning your sibling that they were adopted, somewhat similar to what Charlie used to do to Alan in Two and Half Men. 

If you are the stronger child, you have to deal with an unwritten law, that no matter how hard you been hit, you cannot retaliate. If you are elder child, inevitably all the sympathy will land on the brat. 

But sooner you will both grow older and will get separated either for higher studies or job or marriage. And you are left with memories. 

You will not be in touch with each other quite often, but you know in spite of all the hardships in life there is someone who shares matching DNA with you, and same blood group most of the time, who will relate to your problem. 

You hankered for privacy once, but now you want your peaceful privacy to be intruded once again, but it will not. But, in spite of all those you will still have many more moments in your life which you will cherish till the last day of your life.