My #1 turn off in JAVs? The acting.
The only way I could enjoy acting in my porn would be if the actors were all so good, so skilled that they were able to fool me and I didn't even think I was watching actors. It's the same thing that movie buffs complain about with cinema pieces -- they hate actors who are obviously acting and love the ones who are so goddamn good you don't even think of them as an actor but instead as the character they are pretending to be onscreen.
This is why I like hentai (which is "less real" according to some people because it's a cartoon or a comic and isn't with real people in the real world). When you read hentai, you believe that the women really are terrified; or the men really are clumsy and first-timers; or the girl really is a virgin. I never, ever, ever can buy that bullshit in JAVs. The girl had to have lost her virginity several men before her alleged "first" in her "this is where I lose my virginity" JAV DVD. The girls are always obviously enjoying the sex but not enjoying it that much: they're never, ever showing genuine displeasure or genuine ecstasy. The faces the JAV actresses make when they're not over-exaggerating always remind me of what you look like when somebody scratches a really itchy itch on your back for you. Yeah, it feels good, but it's not the orgasm of your life, either.
So yeah. If more JAVs (or porn on the whole) were just a man, a woman, and a camera on a stationary tripod (so I knew, or could at least fool myself into believing, that there were no other human beings in the room with those two), then I might be more into it. Cheesy acting really kills the mood -- like the dirty talk or the おいしい!^.^ nonsense you guys have already mentioned -- but even regular acting in porn is a mood-killer for me.
WTB: porn with an average-looking guy, an incredibly beautiful woman, both of whom are highly-trained highly-paid professional actors, and who are acting out a sex scene in which the man (for example) pretends to break the woman in and turn her into his personal sex slave.