You’re missing some critical parts of the issue.

What you’re describing and defining is plain old condescension. And you’re right, it’s not a gendered issue. Anyone can be condescending and anyone can be condescended to. Again, irregardless of gender.

I gave been condescended to by both men and women. It was a straight up ego trip of arrogance by someone who thinks they’re superior. It’s a power flex. Pure and simple.

True mansplaining does have a gendered element to it. I grant you that the term has taken on a life of its own and is often conflated with condescension and patronizing arrogance. Rebecca Solnit has said much the same; she inspired the term by her essay but does not like the way the term has morphed.

Mansplaining, as described by Solnit (without the coined term)is a particular kind of behavior based on male insecurities rather than some kind of ego/power flex. It involves explaining either something really basic that everyone knows or something that the explained to person has prior knowledge of or expertise of. The critical element here is that the explainer knows or has been informed of the explainee’s competence in the subject.

So those are the two elements that make it mansplaining. It’s driven off of awkwardness rather than arrogance and the explanation is either something of common knowledge or known/informed of expertise.

In her essay, Solnit described in detail how this guy went on and on about this great book he read while her friend was there repeating over and over, "yeah, she wrote the book. That was her work."

I’ll give another example.
When my daughter was about 4 months old we were at the hospital visiting a relative. I had stepped out to get a coffee and was standing in front of the machine digging in the depths of my bag for change while wrangling my daughter who had decided to make like a worm. As they sometimes do. This guy comes up behind me and says, "the money goes here," reaches around and taps at the coin slot. Irritated and in disbelief I say, "yeah. Thanks."

He didn’t say this to me in a sarcastic tone of voice like he was being a smartass because I’m taking too long or something. Very important. His tone was amiable and helpful. He wasn’t trying to be a jackass.

Nevertheless, I told him to go ahead as I was still digging out change. He smiles politely and tries to strike up a conversation in which he asks if I’m a new mom, announces that he hasn’t had the pleasure of parenting or spending much time with infants. Then he transitions to the obligatory, "motherhood is hard, it’ll get better, hang in there, it’ll all be worth it" spiels to which I repeatedly reply "it’s fine" and then he proceeds to explain to me how to hold my infant so she won’t make like a worm.

What made this mansplaining is that unless you’ve lived under a rock for the last 50+ years, you’re familiar with how a vending machine works. There are also instructions on the thing. Further, having already stated that he wasn’t a parent and had not spent time with infants, he’s got no business giving pointers to someone who clearly has more direct experience.

I figure he fell into mansplaining because her worminess was making him nervous, not being experienced with infants. He was probably afraid I was going to drop her. He didn’t know how to say something about it and didn’t want to come off as a creep by asking if he could either hold her or get my change for me, making him anxious and insecure. Unable to resolve all that internal discomfort, he defaulted to male dogma about being helpful to women, or an attempt at chivalry.

You see an element of this in Solnit’s essay too. The guy had asked them to stay and then most likely felt obligated to entertain them. Then he felt awkward and uncomfortable because he didn’t know what to say and defaulted to explaining something new he had come across, paying no attention to what anyone else was saying (like that it was her book and work) because he was struggling with social awkwardness and being put on the spot.

What makes it patronizing is that default setting men have that women need or desire to have such things explained to them. And yes, it’s somewhat annoying.

I think though, that the main reaction to true mansplaining is mildly annoyed bemusement. It brings to mind some of the bumbling, inept, awkward, and insecure characters of John Clease or Colin Firth. Part of you wants to throw the guy a life line before he makes it worse and part of you wants to strangle him and throw him down a well because he just insinuated that you’re too stupid to work a vending machine. You can fairly easily train animals to work a vending machine. But, being a woman, you’re going to need the paternal help of a man to figure it all out. And, of course, he doesn’t realize he’s just done this.

And there’s the thing. You recognize the guy is just bumblin’, stumblin’, fumblin' … but why is it that the default to resolving that internal struggle is ALWAYS to try to make a woman out to be more stupid and inept that he 'feels' in that moment over the most mundane and random of things? And why do women default to bemused tolerance in the name of polite behavior instead of just nipping it in the bud?

Mansplaining is bizarre and exasperating.