> What I don't know how to handle (as evidenced by some comments here) is when to divulge how much I study / what fields I have a lot of experience in. I never understood where the boundary is between people thinking you are a know-it-all and arrogant, and thinking you are an idiot.

I think the thing to understand, is that non-autistics are very, very particular about the difference between what's inside their own mind, and what's inside your mind. Even on a topic that you may know "everything" about, you still know nothing about what the other person knows about the same subject. Everything on the right side of the below drawing (assuming that you're the one on the left) is in the dark to you, or close to it. And, likewise, everything on your side is in the dark to the other person.

| O O |
| ----- ( inner landscape (fact) ) ( inner landscape (fact) ) ----- |
| | | |
| / \ / \ |

The process of discussion, as seen from the non-autistic person's point of view, is to let you peek into their mind, and to let you see what they know (or don't know) about the topic that's being discussed. And they expect you to let them peek into your mind, and to let them see what you know about the subject. What they are very particular about is that their facts (about the subject at hand) are their facts, and your facts are your facts. Their mental model is to try and align their own thoughts about the subject at hand with your thoughts about the subject. Their goal is for both of you to "see" each others minds, and to bring them into sync, on the topic at hand. It's a process of alignment of two minds, on a particular topic.

| O O |
| ----- ( inner landscape (fact) ) ----- |
| | | |
| / \ / \ |

The autistic person, instead, has a tendency to think that when he has studied everything that there is to know about a subject it allows him to not consider the contents of the other person's mind, because the contents "should" be the same. This is what's considered as "arrogant" by the non-autistic counterpart. To him, when you do this - and I will stress this, even if you know everything there is to know in the world about a particular subject - it's a transgression. To him it's as if you disregard the existence of the contents of his mind. He wants you, and expects you, to consider the contents of his mind, even in the case where it's blank on a particular subject.

What non-autistic persons react to, usually, is the blurring of the line between what's inside their mind, and what's inside your mind. When you see it as if you're just communicating the objective facts of the situation, and "divulging how much you've studied the topic", they view it as a transgression, and as a side-stepping of the natural process of "alignment of minds".

Finally, since your user name has a sort of Nordic ring to it, I will disclose a related poem by the Norwegian poet Haldis Moren Vesaas (if you're not Nordic, just disregard it):

ORD OVER GRIND

Du går fram til mi inste grind
og eg går òg fram til di.
Innanfor den er kvar av oss einsam,
og det skal vi alltid bli.

Aldri trenge seg lenger fram,
var lova som gjaldt oss to.
Anten vi møttest titt eller sjeldan
var møtet tillit og ro.

Står du der ikkje ein dag eg kjem
fell det meg lett å snu
når eg har stått litt og sett mot huset
og tenkt på at der bur du.

Så lenge eg veit du vil kome iblant
som no over knastrande grus
og smile glad når du ser meg stå her,
skal eg ha ein heim i mitt hus.