So basically when everyone you meet is a sociopath, then maybe you're the sociopath.
That Twitch stream really showed it's within his ability to be a decent person (you can say it makes his kahntent boring but that's another thing entirely) when he tries. He's either too lazy to or doesn't give a fuck enough to not be a disgusting asshole when doing something that he sees as his full time job.
This is only tangentially related to DSP's psychology, but still relevant in terms of discussing some aspects of that:
He hasn't ever traveled internationally, he doesn't seem to have any relationships with people, he doesn't travel in his own city/town more than a few yards away from his house, he pretty much wasn't even aware of Netflix until about a month ago.
His 'comfort zone' seems to remain very consistent, this can be seen easily with things like banning/blocking people who are inconvenient as well as deleting games that he doesn't like. Never mind that he never seems to go anywhere and spends the majority of his current life either playing games/streaming or sitting on his sofa watching TV.
It can also be seen with his cooking/food where a large number of his meals seem to be from the same restaurants or the same recipe. While some of this is possibly down to budget, its obvious he isn't really trying out new things in the kitchen very often.
Phil is either incapable of moving outside of his safe zone, or through previous bad experiences in life has withdrawn into the space where he is now. Although he perhaps pictured the famous move to Washington as being transformative in his life, he clearly hasn't been able to (or hasn't wanted to) move outside of his well traveled comfort zone.
It's even easier to see this when it comes to big decisions that he has so far refused to make (for instance, selling the CT condo) and have ended up ballooning in severity. I'm thinking its possible that he might just have a habit of internally turning small issues into giant issues and hasn't yet learned a proper method in how to deal with things.
That's probably the main reason why his videos are boring when he tries to act polite/normal, he's just a boring person who's only claim to fame is some obscure fighting game championship (to add to that its a 4th place title). He isn't well-traveled, well-read or even very good at speaking. Due to the longevity of Phil's YouTube career, he's basically never experienced anything that would force him to adapt at any point in recent history. Things like anxiety/fear/sadness/unhappiness are all normal human emotions which usually make humans adapt to new situations as best as they can. When someone stays in their comfort zone for so long, its obviously only a matter of time until everything they experience becomes negative.
The highlight of his life seems to be the very few instances where he has to go outside or deal with something outside of his control (such as the fire detector inspector man and powerwashing his driveway). When you have no control of anything in your life you're pretty much helpless.
It's little surprise to see Phil become exhausted by his current line of 'work'. It's pretty much the only thing he does. Besides watching wrassling and tv/movies he doesn't seem to have any other hobbies or interests for himself.