It is a very interesting topic when we’re talking about INTJ. So many memes and explanations about the INTJ's (and INTP's) "Death Stare"
The whole explanation is everywhere in the Internet so I won't explain it again. Go googling it yourself. In short, death stare is a condition when INTJ looks impassive, like a devilish glare without evil grin. (I am super-generous, aren't I?)
In this post I want to just talk about the Death Stare from the INTJ point of view. I guess there's quite a bunch INTJs trying to explain to you what's going on inside an INTJ's head when he looks really deadly. I will not give you the similar story (a kindhearted explanation), but I am going to be blunt. The main purpose of this writing is not to ask for an understanding from anyone, it serves anyone's curiosity about what's really happening inside INTJ's head -- my head, more or less.
I am sure if you know the Death Stare, you've read enough basic information about INTJ.
A lot of things happen inside my head*. It forms a quite simple thought process: observation, hypothesis, early analysis, diagnosis, cross-check, late analysis, evaluation, hypothesis reformation, conclusion. I observe merely everything, question the theories and its correlation to the fact, and form hypothesis. In this stage, many observations are rejected without any further processing because they're simply boring. Some are picked up and thrown to the archive to serve as an additional fact/truth for a certain topic. Some are grouped as "waiting list". They wait to be thought.
It doesn't always go like that, some information are quickly assessed and processed, things are getting DAMN REAL INTERESTING, and I couldn't help but maintain the exact position of my body, including my eyes because this certain thought is really interesting! Wait, you ask for an example? Don't. Well.. let's try finding something easy and short. Oh. It's like the human body has a very organized pathway for everything. It's flexible but unchangeable. If you are going to lose weight by eliminating the consumption of carbohydrates, it's totally stupid. Proteins will be converted to provide the energy first. Fat comes after... you lack enough protein to live. In other words, you're dying. Talking about proteins, first you'll lose your muscles, then.. wait. You're going to sleep. Well, you have been warned.
In that state of mind, I usually maintain my eyes barely open, enough for me to stay alert for my surroundings (although most of the times I'll ignore them), and my eyes will stare at a certain point somewhere. It could be chairs, floors, or your eyes.
I have figured out how to position my eyes before zoning out so it will not bother me afterwards.
Basically, it doesn't have any single correlation to you, (if you're unlucky enough to be the victim of the stare). You might provide a good topic (from my observation) but there's nothing to do with you, personally.
Sometimes when INTJ gets annoyed, he will use that Death Stare to imagine killing you with utmost pleasure. It depends on the situation.
Usually the thought will ends at the unanswered question, paradox, contradiction, philosophical discussions, or a task (reading material). INTJ will try to find the answer, or put the thoughts inside a box.
what's really happening inside?
Inside my head, it's like 20 professors from different majors are debating over a topic (yes I was a high-school debater. I wanted to join when I got into varsity, but there's something more interesting that time). They loudly speak, sometimes 5 professors at a time. I am the moderator, I have to listen to them all. One will argue the other's opinion, with a logical reasoning. One will stand against each other, then it's a chaos of everyone's voice. I don't have time to write, I have to listen, interrupt and sometimes "shout" to calm down my head. I don't exaggerate everything. It really is.
Well I said professors solely because they're the best knowledgeable "people" inside my head. It goes without saying, right?
I think no wonder INTJs often stare you like an assassin. Their heads are being tortured by hellish pleasure.