Answer by Moses Namkung:
People I've observed who I've said, "this person is scary smart", generally has the following attributes:
- You can just tell that their brain is processing huge amounts of data at an incredibly fast pace. You see it in their eyes when you converse.
- They generally articulate their thoughts with clarity and efficiency, either verbally or in print.
- Very little bullshit.
There are a couple notes to be made. First, my impression of how scary smart an individual is often comes from signals given during a personal interaction and/or from watching the person articulate themselves (i.e. a video of an interview etc.). This suffers from certain biases (do scary smart people have to be super articulate? .. not necessarily). Second, most of the people I've thought of as scary smart, I've heard of before and they are known to be quite intelligent – and this obviously affects my interactions with them.
But in the end… "scary smart", I think, comes down to a gut feeling that you get pretty soon into your interaction with the individual. There are individuals who you might describe as "very, very smart" or "brilliant" but not "scary smart". But the brilliant ones don't necessarily make you scared. The scary smart ones are the ones who can detect the slightest fallacy in what you're saying and can call you out on your bullshit.