I think I have one explanation that might help.
First, I’m not making any claims that it is the only explanation, or the only issue that rile us feminists up, but it’s a musing I found particularly helpful, so here it goes:
Feminists, myself included, often tend to be very critical of everything to do with biological sex, alternate names for the movement, and casual comments about how feminists should be more “friendly.” I’m tempted to even say excessively, but, to be honest, in general most feminist are not excessively critical. It is more that the average person has little to no ability to pick out sexism and are mostly blind to all but the most blatant cases of it.
I think this difference in awareness accounts for the greatest discrepancies between your average active feminist and the general population, and why feminist are often seen as overreaction.
To give an example for atheists, how a feminist feels when some makes a cliché argument like “why can’t feminists be more friendly” or comments like “there (obviously) are differences between men and women” is much like how an atheist feel when some bring up Pascal’s wager or the kalam argument like it’s the new hot thing.
However, for those who don’t quite get that example, it’s like how some times someone just doesn’t have the points of reference necessarily to understand your position and relate. It isn’t that they are stupid, or can’t understand it. It’s more that they are simply not yet in a position to be ready to comprehend a complex problem like sexism. Just like a student in 9th grade isn’t normally ready to learn about the material taught in grade 12. However, this example fall apart here because sexism is not ignorance. Sexism is propelled and strengthen by ignorance. It does real harm to just about everyone, so to not challenge it when it has arisen is like not correcting someone for using a racial slur.
These outbursts tend to be less anger and more frustration brought about by exasperation. A combination of desire to speak up and make positive change and a defensive mechanism to the onslaught of these question that many active feminists face. I’m aware of it and even then I want to, or actually do, snap out at people who make some of these facile (facile in the sense they don’t capture the true nature of the problem) arguments. Even though I know they probably honestly don’t know any better.