Really? You're easily impressed. I can't think of one teacher from my first 12 years of education that I am confident is smarter than me. I'd also be surprised if not a single one of the people I have taught was ever smarter than me (and hence mistaken if they apply the criteria you propose). But then, I've already expressed my preference for associating 'smart' with fluid intelligence rather than crystal intelligence. Do you actually mean 'knows more stuff' when you say 'smarter'? (A valid thing to mean FWIW, just different to me.)
They were smarter than you then, in the topic area in which you learned something from them.
When you've caught up with them, and you start being able to teach them instead of them teaching you, that's a good hint that you're smarter in that topic area.
When you're able to teach many people about many things, you're smart in the sense of being abie to easily apply your insights across multiple domains.
The smartest person I can conceive of is the person able to learn by themselves more effectively than anyone else can teach them. To achieve that they must have learned many insights about how to learn, on top of insights about other domains.
The previous open thread has now exceeded 300 comments – new Open Thread posts may be made here.
This thread is for the discussion of Less Wrong topics that have not appeared in recent posts. If a discussion gets unwieldy, celebrate by turning it into a top-level post.