Quite a few men and women grew up with men running the show, that's what they were comfortable with. Now that that is being questioned (in spite of their talk about women's special rights, men are still running our society politically and economically) it's made quite a few people uncomfortable. They don't know what their role is, if gender roles are no longer rigid (this applies to both men and women).
So quite a few men (and women) are confused about what a man is suppose to do, so they get frustrated, and get angry and since feminists are a good target to vent their frustrations and rage on , that's what they do, spew rage at feminists. We hear from quite a few of them on this forum.
Some men have lost money in a divorce, lost control of their families or lost custody of their children; or their ex's are using their kids against them or withhold contact from their children to punish them. Again, it can't be because of the way laws are interpreted by judges and juries, or the sexism of judges and juries, these men blame feminists for the loss of their kids and money. I"m willing to bet the majority of their ex's wouldn't call themselves feminists, but since things didn't go their way, they're calling their ex-wives feminists. You hear from them on this forum quite often.
There's hundreds of web sites supporting men who have lost their money/kids in divorce, and the majority blame, feminists. It's easier to blame feminism than to admit their families and friends are so sexist they don't trust them to be a parent. I think men and women should share custody, and have a shared account that is only used to pay for child expenses, but supposedly feminists only want women to get everything, no way we would actually want what's best for the children and what is fair. This is a popular refrain on this forum.
Quite a few men are angry that they can't act like they always have at work, and like to label pc stuff that varies between borderline to downright nasty: telling sexual jokes, putting up girlie pictures, telling women they look good (while staring at their breasts), talking about how emotional women are when they are pms'ing (implying women can't handle pressure or authority), talking about how unreliable women are when they have kids (since women are assumed to be the primary caretaker), talking about how women should only work at home, talking about how women who work outside the home are "easy", touching a woman, pressuring a woman to be alone with them or see them outside of work, asking a woman to have sex with them, etc. Some men hate it that they have to watch everything they do at work, sorry guys, but I'd rather that then have to deal with the sexual harassment I've witnessed on the job.
Some men and women come from abusive/oppressive homes, and really believe women are less than human, and are stupid, inferior, and should be quiet, subservient, and obey their husbands, no matter what. Of course, they hate feminists for questioning their way of life.
Some men and women are conservative in their view on gender roles because of their religious beliefs and/or political beliefs, and don't want to examine gender roles or gender stereotypes. They don't want to question any other ideas either, but questioning the role of a man and woman, and marriage seem especially threatening to these people and they are fighting hard for their conservative way of life. And they are fighting a nasty battle, using their religious views and rigid gender stereotypes to combat gender equality. The bible beaters aren't around here as much, though.
Finally, men and women are upset about how domestic violence and rape laws are being implemented. Some of the domestic violence laws are being misused by some women, which is so sad, when some women and men desperately need protection from their present or ex-partners. I don't know how this can be addressed when some men and women need serious protection from violent partners and ex-partners. As far as rape goes, so many stereotypes exist about rape, it will take a long time before it will ever be resolved. The sick idea that men can't be raped or that women deserve rape are two stereotypes that won't die, but we can try our best to kill 'em. Men and women have a real reason to be angry when someone ignorantly says boys or men can't be raped or would "enjoy" it. I hate that stereotype as much as the rape myth that women want or deserve to be raped (and therefore, tortured).