The only times I’ve ever watched porn, it’s been in the company of same-sex friends (and occasionally some opposite-sex friends, too). But then, I’m female and I don’t find porn remotely erotic in any case; the fun of watching it is to mock it, and the more the merrier.
You obviously haven’t seen the magnificence that is “Police Officer Perez.” 
I don’t think it’s weird, but I do think it is gayer than an explosion in a glitter factory. Getting sexually aroused together implies a desire to quench that desire together. Why they don’t just go ahead and do so is beyond me.
If you are all getting together to watch clown porn then you must all arrive in the same car, of course. 
I never watched porn with one guy but it was OK at bachelor parties or if we were all going to make fun of it. “Hey, I just got this new movie you have to see! There’s this one scene where this guy is supposed to be a demon and he screws her with his tail!”
Back in the early 80’s the college I went to would have movie nights and one time they showed Debbie Does Dallas at one of the school’s theaters (how the student association was able to do this I have no idea). The theater was jammed. A lot of people treated it like Rocky Horror and brought props including rubbers, an Inflate-a-date ™ that was bounced around like a beach ball and bottles of Ivory liquid soap that was squirted at appropriate moments. Having never been to an “adult” theater before I was a little awed to see genitalia displayed in those dimensions. I don’t know if there was any audience participation going on during the movie but my girlfriend at the time was definitely intrigued.
Let’s ask John S. Hall of King Missile.
From “Gay/Not Gay.”
(Personally, I think it’s fine, but I may not be the best judge.)
Don’t forget… they only read certain magazines for the articles.
A small group? Yeah, absolutely weird.
In a dorm room with people walking in and out and cheap beer all around? Not weird.
One night in college we actually had an RA-sanctioned porn party in the study lounge. There were fliers and everything, and I’m pretty sure every guy and girl on the floor (aside from those people who never ever socialized with anyone… you know the type) was there. It was a blast, and I don’t recall actually being aroused.
In defense of my OP 
, this was sharing a teeny Bay Area apratment with only one TV, so If one wanted to watch porn, the other either had to watch as well or go outside. And back in the 90’s the SFO public access channel showed some pretty bizarre porn type stuff, which was fun to riff on.
Me and my buds would watch a few minutes of porn before going out to the club.
We refered to it as a Motivational Cassette
We would then proceed to hit the scene and try our chances for a one night stand… Quite effective, really!
Well, one guy had to go last, because he took 45 minutes to an hour to get the job done.
So, of course, he’s last.
Then the typical R-P-S match - loser goes 4th, next loser goes 3rd, etc.
By that logic any occasion for which a stripper is hired would automatically turn into a giant circle-jerk. I think your second sentence is flawed, from my very limited experience of the matter.
Did you read my third sentence?
Like Roseanne’s Darlene said when D.J. first took up the habit: “Either he’s really, really good at it – or really, really bad.”
Well, c’mon, hentai is very different from US porn. Many hentai have plots and characters and everything, real stories to go with the sex scenes. And some pretty weird sex scenes. Very different from US live action porn, which typically is just two or more people having sex for almost all of the runtime. US porn offers very little to riff on except for the sex, whereas hentai is just FULL of riffable goodness.
Oh, but it used to be (back in the upper paleolithic) that big-label commercial AmeriPorn used to include desperate, pathetic-comical attempts at having some sort of a “plot”; the range from near-surrealist incoherence to gloriously inspired ridiculousness to totally silly pretense of artsyfartsyness was an abundant mockery quarry. The rise of so-called “gonzo porn” after the late 90s kinda left that by the side, but it does still exist.