He says he hates himself, that his life sucks, can't stand most people,

This is a reality that he has created. Every time he states these things they become true for him. We create our reality ,our experience in this life. He needs to understand this. If you want to help him. Get him to realize that these negative things he states are of his own making. You might want to search IQ tags reality creation. I found this very helpful too it is an excellent post from @Satori. http://www.inwardquest.com/questions/60526/a-process-for-creating-positive-situations-and-experiences If you can understand and relay this information to your friend I think you both will find it most helpful.

A little lifehack that has worked for me is not use the word hate. There are thing which I strongly dislike like but not more than a handful that I use the word hate to describe. If you are familiar with the Abraham -Hicks Emotional guidance scale (EGS) you will see that hate is very low on the scale .
I have always said " Life is too short to Hate" or like Fatboy Slim has said in this song "Drop the Hate"
peace

Tell your friend to affirm

You are perfect. You are amazingly, blindingly beautiful. You are strong, vibrant, a magnificent creation. You are an extension, a manifestation of the loving energy that created the entire universe, in fact, you are all there is, and you can do anything. :D

It seems very general so to get to the understanding will take some talking.

Ask him why he feels his life sucks, what does he want to change and how he could change it to be something he would more prefer.

Sometimes we need to get to a place where we feel so sick of how things are that we decide to change our lives.

There are millionaires that were once homeless. They had to hit bottom and get so disgusted with themselves and their lives before they got angry enough to take a stand and say, "No More, I am going to change my life and never have to feel this way again!" They make a plan and systematically change themselves and their lives.

It takes a lot to get to this point of determination.

We can look at life from a practical view or a mystical view. We could say, "Why was I born? What made me come here, this sucks!" That is looking at it from a mystical view of which nothing can change since it is wanting to change the past to have a better present. We can alternately look at life from a practical view, life doesn't suck, only my life sucks. What am I doing that is not working? What am I not doing that would work?

This is for the self but it could be the world. The mystical view. Why is this world so messed up, why doesn't God step in and change it? The practical view, this world is so messed up, what could I do to change it?

The mystical view takes away power, it places it in anyone else hands but your own and says you can't do anything about it. But the practical view says, I have a choice. What can I do to make things better?

There was a little girl throwing star fish from a beach back into the ocean. A man happened along and commented, "Bah! This is a waste of time, you will never be able to save them all!" She commented back, "Maybe this seems a waste of time to you but to this star fish, (as she throws another in) it matters a lot."

Maybe we can't change the world but maybe we can have an affect and change life for some and that does matter.

Martin Luther King did not think equal rights was a waste of time, he let his anger fuel him to do something to make a change. Many presidents and senators and congressmen do the same, they said something has to change, how can I change it?

People that work in food banks see people struggling and they make a difference, maybe not to the whole world but to those struggling people they matter a lot! God bless them for it too.

Do you really want to know the truth? you base the way you see him according on external factor. but is problem might be internal factor. that is why he is frustrated because of the internal things that he does not understand about himself and other. what one think and does to other is often what he does to himself since it comes from that person. you say it is very confusing he also must be confuse, think about it this way if one try to understand and find balence where does he find it outside or inside? in this world things go up and down many time according to people own choice when they made the choice it seam logic it serve them and their desire. to give you example lets take money people created money to help them out now many people live in this world for money they want more and often at any cost some even steal and kill people for it. Does it serve people? what does your soul (mind and heart) tell you about this? if people want more money is it because they have it abundantly? what will they do to other that they would not like being done to them self to get more? it would be logic that they would not do that to other if they do not want it being done to them. yet it seam logic and in accord with the desire at the beginning when they made their choice.

If he ask to keep a eye on him and to be honest with him. is because he feels insecure and want the truth to not be deceive. he might have been deceive more then once in this world the rug might have been remove from under is feet more then once and he seek for balance to not be deceive and fall again and get hurt.

to get frustrated does not help much and to vent with force to the four wind does not help much either.

It would be better to understand the truth and find the proper balance to have abundant life for your self and every one else. to create stuff is not the problem to not learn and correct error and inequity that cause this unbalence and stay trap under your own error is the problem.

Let the children grow eventually they will learn from their error and make the proper correction for them self and for other. Respect the way of other but respect first your own.

Let there be light, be the light that you can be, experience and enjoy.