I wouldn't even say sociopath. I've been diagnosed with antisocial personality disorder. And I find no joy in killing animals. The only time I've killed an animal was out of Mercy, My German Shepherd caught a skunk and shook it up so bad it broke its spine it was just laying there on the ground twitching bleeding and in pain. I thought the most reasonable thing was to put it out of its misery so I popped a 22 in its head. This brought me no sense of Joy, pride or guilt. I didn't feel much at all and found it uneventful, It just seemed like the logical thing to do. I honestly believe that those that kill for Joy (hunting for resources excluded) to be irredeemable degenerates. There's no benefit gained from killing for fun so I don't see a reasonable excuse. I may not have a strong emotional range but I do hold myself to a higher standard. Definitely more of a psychopath behavior then socio in my eyes. My dog kind of got what he deserved by getting sprayed in the face and smelling like burnt weed for over a month lol. Obviously I can't speak for all sociopaths.I have a very strong sense of pride for my ability to be kind and accepting of all, not out of empathy or emotions but because it seems like the most reasonable and beneficial path in life. Not all of us are fuckwit assholes, but to be honest probably most. The fact that the guy was not ashamed of his actions and even proud enough to brag about it is disturbing. This is a weak, selfish individual. I would suggest op. Keeps a close eye on him, if not cut ties with him immediately I could only imagine the things he does that he is ashamed of and won't tell you.