I mean, if he's not fulfilling his duties and is really a huge problem then maybe he needs to be fired by his boss... I don't know how qualified you are to diagnose aspergers (I take it you're not a psychiatrist with a specialty is Autism Spectrum Disorders) or how much you even know about it. Maybe you are right but maybe he just has poor social skills and is an assh*le. And even if you knew for sure is it really reasonable for you (a coworker who is not personally close to him at all) to be like "look you have a pervasive developmental disorder and your brain doesn't work like a normal person's does!"?

It's not really "treatable" in the traditional sense of the word. It is a developmental disorder which means your brain is fundamentally different from the brain of a "normal" person, not like a chemical imbalance or something. Sure he could see a therapist and become more aware of his problematic behaviors in various situations and learn to function better (or more "normally") in society but it's not "treatable" in the way of taking an antidepressant for depression/anxiety or taking xanax for anxiety/panic or taking a mood stabilizer for bipolar.

I can understand your frustration with a problem employee/supervisor/coworker - I'm not saying it isn't warranted. If he is ASD it would be nice to make certain reasonable allowances or to perhaps go out of you way (again, reasonably) to understand that he has trouble with particular things. But it's his boss's job to tell him "hey we can't you have you doing {problem employee behavior} all the time. Please try to do {better alternative} instead". And if he fails to do his job well after this kind of guidance then he should probably be fired. I believe in being compassionate and giving people chances but if he seems not capable of fulfilling his duties after these chances are given then sure, he should be fired.

I don't know what the particular problems here are but I think they should be addressed by his boss as individual problems instead of telling him "we've all agreed you have autism" when you're in no position to even judge that as you are not a psychiatrist with experience in diagnosing autism. Sure he shouldn't be given unlimited leeway for any reason (including autism) as he needs to be effective at his job. I just don't think you are in a position to judge whether he is autistic or tell him that he is autistic even if you think you know.

It seems most reasonable to treat him like a normal employee, instruct him to change his behavior when it's a problem, give him a little leeway in certain areas where it's warranted, and fire him if he's unable to fulfill the duties of the job in a way that is satisfactory after being given sufficient chances. These are the duties of your boss, but obviously he's not fulfilling them. That's not your fault and it's frustrating you, which I totally get... I just don't think you can "accuse" him of being autistic.