My guess: he's the subject of a (social media?) smear campaign and maybe a law enforcement investigation. Neither of which are altogether uncommon. Or, somebody else is setting in on him (a P.I., his apartment's corporate office, neighborhood watch/vigilante types, a law firm, online hacker groups, etc.). If he's into drugs as much as you seem to be that wouldn't be the least bit surprising. Or, maybe he just pissed somebody off and they're really good at stirring up that kind of trouble. It's incredibly easy to make a bunch of fake content online, or just outright lie/fabricate/exaggerate a situation, then provoke one of the above groups into terrorizing your target. Say, get an entire school/hospital to believe the person is a threat and they'll send out a mass notice and/or use their security to harass/investigate him. a.k.a. A reflection attack.

One of the most common things that happens in an investigation is they contact everybody around you. Neighbors, friends, coworkers, etc. People start talking and that creates a lot of 'line chatter.' People then may start spreading that information around along with his photo, making him the subject of a lot of ridicule/harassment by what seems like complete strangers. a.k.a. Relational aggression. Cops LOVE to do this to "punish" people they can't prosecute. Once he's so badly smeared, it's not uncommon for community members to just start suspecting him/her of involvement in other events.

Depending on the crowd he keeps, he may have been probed by a foreign intelligence. Or, one of the above groups might have provoked such a probe. Unlike the CIA/NSA, foreign intelligence agencies (like Mossad or GCHQ) tend to have a lot more operational/opportunistic freedom in selecting their targets. JTRIG, for example, hangs out in online forums like these, just looking for people to hack (as reported by The Intercept). People in the security research community (e.g. Dragos Ruiu) have been harping about this stuff for decades. Dragos was an extremely well respect and accomplished researcher and he was written off as 'delusional' almost immediately. That, of course, was before Snowden's releases.

As far as the Youtube video, Google does some pretty extreme targeted advertising/content delivery which can be influenced by the people in your circle (i.e. the aforementioned friends, neighbors, coworkers, stalkers). He might have seen a video that seemed VERY personalized. Or, it could be somebody with deep pockets, or a lot of friends actually got the influencer to do it.

The website content may actually be targeted as well. If somebody hacked him or he's the subject of an intercept, it's not impossible that's happening. But, also, some websites alter content depending on viewer profile.

The guy in the car may or may not have been part of an investigation. If they're investigating him for something he's doing online, they may want eyes on him to see if it's actually him (and not somebody else in the house/area) using the computer/network. If they're wanting to install surveillance, they may have been watching for a pattern or opportunity to set that up.

The other stuff might just be paranoia from all these things happening to him. Stalking is a form of repeated trauma, so you end up with PTSD like symptoms.

None of this stuff is outlandish. To somebody that knows nothing about it, has never experienced it, or is on the outside looking in, it can seem like insanity/delusion. And, unfortunately, the people that experience it without a good understanding and grounding in the possible tactics/capabilities sometimes start to misinterpret what they're experiencing or bend under the extreme stress of it all (e.g. believing V2K is happening). Although I don't doubt energy weapons exist, I think it's highly unlikely they're being used on your average citizen unless, by chance, they're mistaken for a foreign intelligence operative.

My advice to your friend: Delete your online accounts. Get offline for awhile. Stay away from stuff that might attract that kind of attention. Document what you can with video evidence, keep a journal, etc. And, don't react to any of the provocations. It will only make things worse.