How to spot a sociopath/psychopath?

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Recently I've been trying to figure out the workings of mental conditions. A coworker of mine has this sort of smirk whenever I see him/during our brief conversations and it tugs my balls sometimes for some reason. I've come to the conclusion that he's some sort of sociopath, but I could be wrong. Are there any other cues out there in terms of body language and in-conversation that can determine sociopathy/psychopathy?