If I could give a short list of hero turnoffs, this is what my list would include. But having said that, I can say that a good author can make you love a book despite those things that would normally turn you off. I can admit that I have read and loved a book with a hero who fits most of the the below. I don't mean to offend anyone who may disagree with me. This is my two cents, for what it's worth:
Duke of Slut: he has slept with every woman he knows except his mother, sister, initially the heroine, and possibly his best friends' wives. Personally I think these kind of characters are users who objectify women. They don't care about most of these women, they just want to get off, and to me that's wrong and makes the character unlikable. I am not saying that all heroes should be virgins, but I'd like to read more celibate heroes who respect women beyond just wanting to sleep with them. I have found that a lot of these guys may love having sex with women but most of them probably deep down don't like women as much as they might try to believe they do. The Naked Duke by Sally Mackenzie really impressed me because the hero (virgin) actually recognized that while he was using a woman to fulfill his sexual needs who was no innocent (widow or married lady) or using a prostitute, he was really using someones sister. And having sisters, he couldn't bring himself to do that. I think that romance readers love the appeal of an experienced hero who knows how to please a woman, but he had to get there by using women (either women of loose virtue, or perpetuating the system of women enslavement called prostitution.) Forgive me, but I have strong feelings about prostitution, and if you watch or read historical accounts, prostitutes, even high class courtesans, typically had very short, unhappy lives, and most of them succumbed from disease. I do like when the writer makes a point of indicating that the hero does attempt to protect himself from disease, but the more people you sleep with, the higher probability of catching a venereal disease was and still is. In general books with the Duke of Slut leave a bad taste in my mouth. Even if I like the book, I'm not too happy with this. With rare exception, if the hero has some emotional pathology, it makes more sense. A good example would be The Devil You Know by Liz Carlyle. I love it when the hero finds out the heroine is not a virgin and shrugs and says, neither am I. Bravo.
Mister Testosterone Toxicity: his testosterone levels are so high, that it is killing his brain. AKA Uber-alpha male. While I don't hate alpha males, I believe a little alpha goes a long way. I think it takes talent to write this character really well.
Sir I Believe Everything Bad About the Heroine Despite All Evidence to the Contrary: he is usually a duke of slut but for some reason hears rumors that the heroine may be less than innocent and decides she's a complete whore. This is also found in books with the Big Misunderstanding. Instead of just going and talking to the heroine for about five minutes he goes on the warpath. Most of the time I don't like books that much when they feature this hero.
Lord Double Standard: usually a Duke of Slut who wants a perfect, innocent wife. Like you deserve one. Also found as the guy who is far from perfect but is looking for the beautiful, connected wife because he deserves no less than that, and knowing he will probably be bored to tears if he does get Mrs. Perfect. This guy is often a snob in historicals because he's an aristocrat but the heroine has humble origins. I have also seen them in contemporaries.
Mister I Cannot Get Married Because Marriage is Not For Me: even though he has found his true love, he just cannot fathom the idea of actually marrying, because it's the end of the world. If he gets married he will just die. I know a lot of guys in real life has commitment heroes. I know I do too, but I don't hate marriage. It's so played out. I wish that this dude had a truly legitimate reason not to marry, but most of the time he doesn't. He want to have sex with heroine but he doesn't want to marry her. It could be because of any of the above or some other reason that makes perfect sense to him but not the reader.
Mister For Some Reason I Feel its My Right to Torture the Heroine. He does this in various ways: A. Saying horribly mean things to the heroine (especially hitting those sensitive areas). B. Parading his ex-mistresses around in front of the heroine. C. Doing something really mean to the heroine just because he can.
Mister Adultery. He believes it's okay to cheat on his wife because he doesn't love her, or he is forced into marriage, he is unfulfilled, he is afraid he will love her but won't feels he won't love his mistresses or lovers. Also the hero who thinks it's okay to sleep with other mens' wives if they don't keep them satisfied, or don't get caught, or just doesn't care. Ever heard of the Golden Rule, buddy?
Mister Thick as a Brick: this guy is so dumb he can't think himself out of a box. Thankfully this is rare. It's really bad when the heroine is also Too Stupid to Live as well.
I think these are the main ones I don't like. I think that if the hero is tortured, he will show some or many of these traits. Hopefully the writer has built a foundation of realism and a background that substantiates the reasons why he is doing these objectionable things. Sometimes I have to keep reading to find a reason to like the hero. If the writer can take a serious jerk and make me feel sorry and even like him, then I am definitely impressed. Some writers do it all the time, Diana Palmer for one, and I like most of these guys, and some fail miserably.
Again this is just MHO. Everyone has their own buttons that get pushed.
