But you can tell pretty quickly how smart someone is.

Aside from recognizing obvious idiocy, you really can't, though. There are all sorts of reasons, from behavioral affectations, speech patterns, and a simple unwillingness to engage in the way you commonly do in order to judge someone's intellect, that can easily thwart your ability to accurately judge someone else's intellect correctly.

For instance, interrupting people to reply to their thought isn't a show of intellect, and it's fallacious to think it could be. You assume that because you were doing that, you were the only one who could "read minds". Even people with average, possibly below average, intelligence, can guess the coming sentence from context, knowing a bit about the person, and the first few words. But most people are also smart enough to know that interrupting people is offensive, so they don't do it.

I'd assume any real genius level intellect would figure this out when their age is single digits, because I did. Does that mean I can assume your intelligence is lower than mine because you clearly hadn't figured that out?

The answer is no. I can't. That would be a foolish assumption, and if I made it, it would be more to reinforce my sense of superior intellect than because the information I had demonstrated anything definite.

But without question, if you think you know how smart someone who isn't clearly suffering some sort of mental deficiency is, within a few minutes--or even after spending some time talking to them every day for a month--there's no way you're not making unwarranted assumptions. There is no method to accurately gauge other people's intelligence through conversation without a great deal of time spent with them, generally intending to test their intelligence, and their willing or unwitting aid in that, without which you'll still fail to gauge them accurately.

You're simply assuming a negative from the lack of proof of a positive. This isn't a situation to which Occam's Razor applies, though. That's obvious, which is fairly well proof that you're making the assumption sheerly from desire to do so.

I'm sure plenty of people who you tried to engage in conversation to gauge their intelligence probably thought you were kind of an idiot, because it looks dumb to be offensive on that level. Conversation is probably the situation where emotional intelligence crosses over with IQ most directly, and a lack of the former will make you seem dumber. Your self-description is a pretty straightforward admission of weakly developed emotional intelligence.

Anyway, that you can't judge high intellect that easily in conversation is logically unimpeachable. Easily understood by average minds after some serious consideration. No additional level of intelligence can work around the fact of it. The world's smartest person can't do what you think you can do.

Thinking about what that means about you as a person would probably be helpful with your toxic personality issues.