I'm not really a fan of porn movies but I have seen enough of them to definitely know what I don't like.
1) Close-up scenes showing a girl with pimples on her butt
2) Close-up of a shaved pussy with some stubbles that are growing back
3) Some japanese porno movies: you know the one where the images showing genitals are totally blurred
4) Japanese porno movies: when the girls are whining like pigs on their way to a slaughter house.
5) Seeing ugly skinny boys (like the young Tom Byron), or morons (like bikers with a lot of tattoes) performing with beautiful women
6) Scenes involving violence (simulated rapes, hard sex involving lesbians fisting each other)