Respectfully disagree. Unlike you have.
Here's how I'll disagree. I hereby claim the following premise: that grabbing someone's ass is just grabbing someone's ass. At a minimum. Inherently. It may or may not be "harassment" depending on other particulars. And it is definitely not clearly inexcusable. Not always, not inherently. More specifically, grabbing someone's ass WITHOUT their explicit consent beforehand is NOT necessarily harassment, and therefore is not necessarily inexcusable. Again, it's just grabbing someone's ass. (Oh noes!) WHETHER it's bad, whether it's harassment or "inexcusable" depends highly on the context, the environment, and the two people in question. Indeed, the word inexcusable means it cannot be excused. But clearly if say a handsome hunky man grabs a pretty woman's ass at a bar or on a dance floor one night, there's music, dancing, alcohol, people are feeling frisky or lonely, looking to hookup, etc. and the guy finds the woman attractive, and especially if she finds him attractive (this is key), and she's in the mood (this is especially key), guess what? She may excuse him. That's a strong bet to make. It's happened before, it's happening now I'm sure all over the world and it's going to continue to happen for a long time into the future. People have sex. Behind closed doors they get nekkid and fuck like rabbits. And for every time you hear a woman saying in public she wants to be treated with respect, treated like a princess, be respected intellectually, etc. you'll hear another woman (possibly the same woman in a different context or mood) saying she likes to be hit on because it makes her feel more attractive and desirable, she wants men to touch her, she wants men to be aggressive and dominant with them and she sometimes, deep down, honestly, she wants to set all higher-ordered thought and pretensions aside and get fucked long and hard like an animal -- the whole "ravished by a pirate" fantasy, or "swept off her feet by a rich handsome witty man" fantasy, to cite just a few among hundreds of similar variants and archetypes. (I'm not making this stuff up, fellow HN'ers, this is fairly common out there outside academia and software engineering-land.) It's all over the freaking web, in books, private lunch conversations, women's magazines, etc. And so for a variety of reasons, yes, sometimes due to men with bad social/romantic judgement, and yes sometimes due to inebriation, some ass grabbing goes on. And sometimes women like it. They fantasize about it. And sometimes they do NOT. But to call it always inexcusable harassment is clearly in violation with the facts of the real world. Is it happening more than it should? Probably. Is any real harm done? Not unless you have a very ethereal and non-physical definition of "harm". Which some people do, of course. And that's the larger, meta-problem that many of us have with discussions about this topic. It's not that we don't agree with you that sometimes men do inappropriate things, sometimes. They clearly do, sometimes. But it's this repeated meme some folks propagate that merely to touch someone constitutes rape. That a momentary butt-in-pants squeeze is somehow violent or life-altering or traumatizing. That flirting is always harassment, and so forth. There's a whole lot of survivorship bias which occurs. And there's a whole lot of nuance and shades of grey, that exists out in the real world, that I think gets sadly glossed over.
Heck if I went to a bar or dance club at night and some woman grabbed my ass my reaction wouldn't be, "Oh no! That's inexcusable harassment. I feel so violated. I'm going to call the police. I'm being oppressed by the female gender again." Instead I'd be more like, "Well, hello ladies!" and feel complimented physically. (And how I'd respond would depend heavily on whether I was single or not, etc.) And again, of course, it depends on the situation -- it would be less appropriate in a corporate office setting during a workday, by a stranger, for example. But at an office party, at night, alcohol flowing, loud music, etc? Heck yes.