1) apparent non consent by a participant
2) boredom
3) padding (i.e. unreal about the experience).
Look, watching certain things (scat, men on men) do nothing (or worse) for me. Other activities (foot fetishism) don't repel me, but I do find them boring.
But I question the point here. Who cares what I like, or don't? Ditto anyone, even an ubber hottie like Dallas Rain.
I enjoy watching MMF bisex porn, but don't like it when it's obvious that the guys are more into each other than the girl. A lot of those movies are really gay porn with a girl added in for window dressing. No thanks.
In fact, it's very rare to find a bi porn that starts out totally straight --two guys fucking a girl-- and veers into guy-on-guy after the girl has been thoroughly fucked. Often those movies start out with two guys making out and the girl "catching" them. That's a boner killer for me.
Every MMF scene should include plenty of DP (or DV, DA).
And it drives me crazy to watch a guy get fucked in the ass (either with a strap-on or a cock) and yet his cock is totally limp. If you can't get hard while being fucked in the ass, you don't deserve to work in the porn industry.
Sorry for the rant... but I have strong feelings on the topic of porn. Given the enormous volume of porn in the world, it amazes me that all of the bisexual stuff is so fucking awful.
I don't like spitting at all, especially not in each others mouths.
I don't like tattoo's so I'd rather not see them.
I like moaning and screaming and the like but no dialog please.
I do love:
Pegging
two girls crotch to crotch
humiliating men.
My favorite things to watch are bjs and cowgirl or reverse cowgirl. I DESPISE it when they are going at it in these positions and they show a close up of the dude's face and he's moaning. That kills it for me.
I also hate when in cowgirl position and the guy feels like he has to do that power speed thrust from the bottom. Let the girl do her thing in that position.