This is an interesting and funny discussion.
The truth is that most of you cannot do what you claim. You’d pick out the obvious psychos, most likely, the people who drool on their chins and hold wild and noisy conversations with imaginary beings and people who aren’t there. Anyone can do that.
But you’d also pick out some totally harmless, inoffensive and lonely neurotic who’s miserable because he hasn’t got a friend in the world (who could be any one of us on certain days), and who feels and looks worse and withdraws some more even as you reject him, or who’s physically afflicted with a disfiguring disease, scarring or other deformity.
And you’d totally fail to clue in to the BTK Killer , the Green River murderer , Ted Bundy and any number of other past and present serial killers who do what they do for as long as they do it because they appear to be so normal. And don’t pat yourself on the back because you happen to spot a mugshot or courtroom photo and “know automatically” that the person is guilty. After ten or twenty years of killing, these people probably do start to look different, and everyone looks guilty in a mugshot.
This is why parents have to teach kids that “stranger danger” doesn’t mean ”creepy-looking stranger danger”, it means “anyone you don’t know” and maybe someone that you do know.