I didn't put any words in your mouth, these are the extensions of your reasoning -- you simply haven't considered the full weight of your positions and so these conclusions are a surprise to you.

Let's give you the benefit (a huge one) of the doubt here, I'll consider fully and without prejudice everything you're saying:

The statement you make is essentially that all behavior has an explanation behind it, no matter how distasteful or uncivilized. Fine, agreed. First, what is the value in pointing out this obvious conclusion? The only logical counter position would be to claim people have random and inexplicable behavior, a position which practically nobody holds in full sincerity.

You then continue to say that because behavior has an explanation, that behavior cannot be sexism. Literally, if some behavior can be explained by a surface comparison to animal behavior, or by similarities to vague concepts in evolutionary psychology, then it can't be sexism. Let's even accept your very unscientific and highly dubious observations about Cancun and male behaviors, and conclude from this that all males have irresistible animal instincts which compel them to act offensively and crudely.

We have two things here: first, only behaviors which cannot be explained in any other way can be considered sexism. That means that the only behavior which is sexist is the behavior which occurs when a person, in their mind, has the thought "I will now enact a sexist agenda" or something like that. If, for example, a person thinks "it would be okay to go and lick her tattoo" that is not sexist, because it can be explained as a result of poor socialization combined with repressed animal sex urges.

Second, we cannot complain about "natural" behaviors, because after all, they are natural. You might as well complain that it's not a full moon every night, or that the Sun is too bright in the Summer months. Tough, that's nature.

1. Only behavior which is motivated by an explicit intent to be sexist is sexist.
2. Behaviors which can be explained by appealing to "nature" or "instinct" (natural behaviors) do not merit complaint, and efforts to change or curb them are misplaced.

Therefore, two conclusions arise from this.

First, nothing is sexist! All behavior can be explained by appealing to base and instinctual motives. Sexual harassment in the workplace is unavoidable: what do you expect when you put a man next to or above a woman he finds attractive, for eight hours a day? Sexual discrimination in the workplace is also not sexist: it's not a discrimination against women, it's just a natural and active desire to engage with other males. And the situation described by the OP is also not sexist: those men aren't being inappropriately aggressive towards her because she's a woman and they don't respect her boundaries, it's just because they're sex-starved losers!

Second, and even more stupid: bigotry doesn't exist! If the standard for sexist behavior is very specific and limited intent to be sexist, then by analogy you can show that the standard for e.g., racism, is the same. And per the first conclusion, there then is no racism. Or homophobia. These are, after all, very natural expressions of revulsion and disgust for people not like ourselves, and we cannot be faulted for our instincts. Why, these very instincts are what brought us out of the jungle!

A third, less obvious conclusion, is that nothing can be done, or needs to be done about any of this. Women, don't like being manhandled? Don't go to bars where there are males, they can't help themselves. Non-whites, don't like receiving dirty looks or beatings? Stay away from white people, they have a natural revulsion for people not like them.

And whatever you do, don't complain! It's natural and to be expected!

So then, if you can't complain about it, if the behavior is completely natural, then the obvious conclusion is that if you are subjected to offensive-but-natural behavior, you share responsibility for that because you could have prevented it. After all, you have a brain woman, you could have predicted getting manhandled by a bunch of nerds! And everything else I "put in your mouth" is just a little bit more absurd than this. (But only a little, because this is a pretty stupid position to begin with.)

What you're employing here is a logical fallacy called appeal to nature, which in general is an appeal to something that is irrelevant. You haven't demonstrated that it's relevant at all to consider what is natural, even if we allow for your wildly exaggerated notion of nature. You are also being lazy and offensive.