After giving this subject matter some thought, I don't think the person I mentioned had mental illness; it just doesn't look like mental illness in any way once you examine it in detail. I actually spend some time reading up on NPD or Narcissistic Personality disorder, just now, and the person I mentioned would not fit all the criterion, nor can the disorder really characterize him or his actions. Psychopathy is a general term, I mean people just use it to describe anybody who does something which they consider really inappropriate. Anti-social personality, well no, the person had friends, don't really think they liked him much, but it wasn't that. You were right in saying the person was a POS, I think at some point he realized he could get away with things as long as he has the right excuse after the fact, or simply ditch a social group for some time until they are no longer angry with him. I remember way before this whole thing started he used to talk major thrash about others for no apparent reason, I mean people who did nothing against him in any way.
Here is a list of what the things the person did so you can judge for yourself (some of these are repeats of the things I mentioned in my previous reply)
beat up some guy, later gave the excuse that the person he beat up was harassing some girl, I think he went to jail for this one
talked major thrash behind one of his close friends back for no reason
basically used a person to get money while pretending to be his friend
took his mom's car for a joyride while having a suspended license, crashed the car on 2 occasions, both times told the investigators the car was stolen
punched several people for no reason while his friends were around so they wouldn't try to fight him back
attempted to punch or wrestle a person who was a lot more stronger than him and got beaten up badly in the process
walked around with a pocket knife going down the street and slashing every car's tires on it
tried instigating a fight between 2 people over a minor disagreement
succeeded in instigating a fight between 2 people - he did not get anything out of it
beat up some old guy, later came up with an excuse to why he did it -again did not benefit him in any way
tried to get one person to sue his friend over some minor scuffle -the person never sued but this would not benefit him in any way
These are only the things that I am aware of, I'm sure there's more, but you can see the general pattern, in most of these actions he hurts someone while not really benefiting much and
@TheLordOfChaos201 as far as I know he was not having a bad life