Wow, Lee, that's both a very good question and a quagmire.

This may be irrelevant to your specific question at first, but consider this. Each of us may have personal distinctions and reactions to what we classify as "obscene," but is there a consensus? In terms of the law, there has to be, despite it changes over time. Setting legal issues aside, I say doubtful (fortunately or unfortunately). This for the same reason it gets stickier when you ask individuals...

First what's "obscene" is terribly subjective, much less an intellectual/ethical thing than people would admit. It comes from a gut reaction, and then we rationalize it, ha! Me included. I don't think even the most "obscene" people in the world would agree on what's obscene.

Grittier and more to the point, and denied by many, is that ALL of us have some kind of sexual hangup or two, whether major or minor. Of course this influences what we think is obscene. Sexually "liberated" or not, people might not find this to be favorite topic to discuss because it exposes things we don't want to look at and/or don't want anyone else to know.

That said, my opinion of what's obscene on a porn site is anything where people are hurt/abused/endagered...emotionally, mentally and physically. An obvious one child abuse. The trickier one is just what Jacob said. In submissive/dominant situations, there's a fine line but a distinct one between fun, enjoyable play and despicable, hurtful and dangerous activity. Any healthy person knows that point - it's the "STOP" point. All I can (or could) say is how I react when I see something. Sometimes I've seen movies of very hot guys doing things I thought would be hot to me but instead find something isn't working. It must be either I just don't get into it, or I'm sensing something that is truly destructive and terribly disturbing, and that really concerns me.

More obscenities depending on who you talk to:

Piss turns some people off. Turns me on tremendously. Piss is cool. Piss is like cum in big amounts. People think it is dirty when actually it's sterile. While it supposedly carries far less HIV than semen, it's still clearly a body fluid that carries possible disease (if someone is sick) and medications or drugs a person is taking. So I'd say don't knock it, just be smart.

Shit is a double edged thing. Taboo for sure. Can't even really talk about it here. Also more popular than most people realize. It's indisputable totally absolutely disgusting - or it can, yes, be wonderfully erotic, depending on many things.

Ear wax and head cheese (barf!!!!!!) is the grossest most disgusting things people do in sex in my opinion. I can't understand why the creepy, deafening sound of someone's tongue in your ear or the taste of someone's earwax would turn anyone one, but I guess it does. I can't even talk about the other... To me they are both obscene and I would not put it on my sites. But no harm done if other people like it, even though it is really hard for me to admit. Happy day.