Is it just me?
I find the first three posts in this thread to be incredibly funny.
Q: How do I tell my friend that I think he's X for reason Y?
A: "Friend, I think you're X for reason Y."
Q: Yes, but how do I tell him?
Is it an NT thing that the questioner could not perceive such a direct, clear and obvious answer? I think he thought it was a restating of the question.
I can tell you from personal experience that being subtle is not going to work. People tried that with me for years and all I got from the conversations was that they seemed significant and I had the feeling there was something important they were trying to tell me and for some reason they were telling me irrelevant stuff about autism and aspergers.
The message only sank in when I researched it very intensely after the schools pushed me to take my son for an evaluation after which he was diagnosed with aspergers. As I tried to understand how this label could possibly fit him, I saw that in the same ways it fit me, and then I suddenly remembered years of "hints" from people that "went over my head." Even then I still was not sure and I had to call one of those people to verify this conclusion.
The thing is, as soon as I was old enough to go outside my family, people started to treat me badly for being different. So I wanted above all not to be victimized. So I adopted a strategy of trying to hide my socially unacceptable differences as much as possible by doing little and avoiding contact and also to be as quietly threatening as possible so they would fear the potential consequences of aggressively teasing me. A first couple of decades of that approach to life does not prepare you to hear "you are really different from other people in this named way."
Also, I think the traits run through my maternal family and the culture of that family is all about suppression and denial. Their motto seems to be "You have to fake it enough to make it or you will fail utterly and by failing bring attention to the defects in the rest of the family, so hide it, or be gone."
In any case, it may be that your friend will have a hard time hearing it. Or not--that may have just been me.
If you really want to help it might take some work. One of the least successful attempts to tell me that I can remember was by another aspie who stood near me while I was eating lunch and said in a very projecting voice "there are all these autistic people walking around who don't even know it." I thought, "why is she trying to be overheard like that? Who can that message be for?" Absolutely did not have the first inkling of a hint of a clue that she might mean me!
If you can get a copy of Tony Attwood's "Complete Guide to Asperger's Syndrome" and read through it with your friend, that might help. But you are going to have to be very clear and open about why you are doing it and your intention to be a helpful friend and that you are specifically trying to answer the question about what is wrong with him. But those are things that would help me, with my personality--your friend may be different.
I would love to hear how it went, if you do try.