1) The implication is some sort of circle-jerk: definitely gay, even if you're watching porn together.
2) Dude in the corner is a loser, but NOT gay. It's not too different than the way all of us get off (to vids) watching others fuck...I couldn't do that "live", though!
3) NOT gay. I've never "shared" a woman with another guy, but the thought of it is a bit of a turn-on....if we simply take turns or stay on different ends.
4) Now we're reaching my personal limits. I couldn't be at the same end with another guy.....
5)....and certainly not in the same hole
As noted by several others, it's "gay" when you're turned on by the other guy, when you get off with a penis in your ass or mouth, etc. The opinion part comes in when you start reaching your own limits. I couldn't handle a #4 or #5 scenario because being that close to another dick would instantly deflate me. As The Greaseman (a controversial radio personality) once said, some of the friction in those scenarios is coming from the other guys cock. And that's too much for me.
On the other hand, Ron White has pointed out that none of us like limp dicks in porn.....we want to see massive throbbing cock! So bah, I guess we're all a little "gay" by that definition!
Just random thoughts from a newbie. Fascinating topic, thanks for bringing it up.