Only doctors can make valid diagnoses. Nope, it does not matter if you have known the subject since he/she was knee-high to a grasshopper. Your opinion is not a diagnoses.
The person who is bandying about the terms "Psychopath" and "Sociopath" probably does not know doodly-squat about either. They may be trying to sound smarter than they actually are. A more precise statement on their part would be, "I cannot get along with that person....and I don't think I am the problem."
Co-morbidity is common when discussing mental illnesses. In traditional illnesses, a stomach ulcer does not imply an increased risk of, say, tuberculosis. That is not so in mental illnesses. A diagnosis of ADHD significantly increases the risk of anxiety/depression symptoms. A person who is OCD may have symptoms of Opositional disorder or other "regulation" dysfunctions. Nice clean cookie-cutter diagnoses don't happen all the time.
It would be a rare Psychopath who did not occasionally show some of the symptoms of a Sociopath and vice versa.
CommonalitiesBoth disorders share a "lack of empathy". Very few people have any problems with The Golden Rule, i.e., Do unto others as you would have them do unto you. For Ps and Ss, The Golden Rule is opaque.
Sociopaths: In a word, Sociopaths are dys-regulated. They cannot keep their train on the tracks. Their social failures are massive train wrecks. If one were to pick a crime that was emblematic of a Sociopath, it would be a mass shooting.
It is difficult for them to hold down a normal job. They radiate prickly, irritated vibes. They seem oblivious of the effect their "twitchiness" has on others. Consequently, they develop persecution complexes and paranoia. Do you see how that comorbidity thing comes into play?
Sociopaths are capable of small crumbs of empathy under tightly controlled conditions....they may have a significant-other, for instance.
Some psychologist think that sociopaths are formed by exposure to trauma (bullying, sexual abuse, etc) during the patient's formative years. There is some possibility of rehabilitation if the sociopathy is a maladaptive response to trauma. The rehabilitation effort is based on replacing the maladaptive responses with more effective responses.
Psychopaths: In a word, Psychopaths are actors. They are completely devoid of empathy but have learned to "act" the part. Their failures are "off-mike" failures. They stop acting when they think the curtain is down and display their true selves. An example would be a politician who abuses their security escort and makes them carry luggage when there are no reporters present. If one were to pick a crime that is emblematic of a Psychopath, it would be that of stalker/serial killer.
Psychopaths can be fabulously successful at business and politics. They nearly always stick to the script. "Normal" people can be devastated by cataclysmic news and go catatonic. The Psychopath is not personally impacted and can act more empathetic than the healthy person.
Psychopaths are incapable of even the smallest crumb of empathy. Most of us have some sense of belonging to a family and a tribe. To a Psychopath, there is no "family" or "tribe". To them, humans elicit as much empathy as the empathy you have for the mosquito you just slapped.
Some psychologist think that Psychopaths are wired wrong from birth. They believe that inability to feel (sense) empathy is no different than red-green colorblindness. Odds of rehabilitation are nill since the product was wired wrong at the factory.
Is this information useful?
Not really. Most people do not use the terms with precision. All it really means is "I don't get along with that person." It is futile to read more into the words than that.
There may be some entertainment value in looking at various politicians and other public figures and trying to decide which ones are Sociopaths (few) and which are Psychopaths (more than a few).