It's totally normal to get bad vibes or feelings from people. The oldest pathway in our brains, sometimes known as the Lizard Brain is primed to read the signals we unconsciously give out. It's a throwback from the times when we lived among predators.
So, a person can be extremely charming or whatever but your subconscious is seeing that their smile doesn't reach their eyes (for example) so you feel wary of them in the way you can't put your finger on.
I've seen psychopathy used as an example on this thread, and my word yes they can do horrific things (not all will, but none of them will give a shit about you either). So, when people here have said they feel awful but they've felt it about children (no, not babies eyes) then it's absolutely not impossible. Psychopaths are born, not made. Nurture can play a huge part in HOW that psychopathy plays out in life but they have physically different brains.
A control group of non psychopaths and a group of psychopaths were put in an fMRI scan which is basically an MRI but functional (hence the f) which means you see a brain responding to stimuli in real time. They were all showed distressing images. The psychopathic brain showed less grey matter in the frontal lobe (your personality) the limbic system (emotional regulation) they have a much smaller amygdala (the fear centre of the brain) and a much larger nucleus accumbens (the reward centre of the brain) the control group showed totally expected reactions.
So, psychopathy (sorry, ASPD as it is now known) is not a mental illness. It's defecits in the brain itself. However, there are two types of psychopath. Primary (no empathy, no fear, superficial charm etc...) and secondary who are thought to be those who have brain tendencies towards it but nurture plays a bigger role. Secondary do feel fear, remorse yadda....
So, yes, you absolutely can pick up on the dead behind the eyes thing without even realising you have. And yes, dead behind the eyes is a real thing and noted beyond the Hare Test which is the gold standard test for psychopathy. Other things are taken into account like childhood behaviour and a dead eyed stare.
None of it is woo, it's how we are supposed to be.