I think we've all met someone at some time that we - for whatever reason - take an instant dislike to.
I'm pretty sure it's not because of the persons colour, race, disability, religion or political stance, but something deeper and instinctive that says 'watch this one'
Conversely we've also met those we feel an instant affinity to, again just some instinctive brain function harking back to when we lived in caves
In both cases that 'first impression' can turn out to be wrong, but it still happens . . . as Pierre says, it's human nature.