Warning: anecdotes ahead. It has been mentioned previously that harassment of this nature is wildly unreported. I can say from my own experiences that I have mentioned, in addition to at least one other case that I did not (not to mention the far more numerous cases when I worked in hospitality and office administration), only one was reported to management. It was dealt with in-house, and never went further than informal conversations that I can recall.
I didn't mention this in my last post as I cannot conclusively point to it being due to inherent sexism: the end result of that meeting I brought up was that my contract was terminated less than a week later. Up until that point, no issues regarding my performance had been raised, and my boss did mention explicitly that the meeting in question was what prompted the decision. I was told that, 'we want your departure to be amicable. The scientific community is a small place, you know?' In other words, if you make a big deal of this, we're going to make sure your future prospects are bleak.
I didn't report that. I didn't report the time that a fellow PhD student expressed his genuine surprise that I didn't know the process of obtaining government approval to work with children (his words: "but you are a woman, you should know how to look after children."). When I worked in hospitality, I never did anything about the comments made to me by men, or even the time one guy decided to place his hands on my hips and feel me up to 'diagnose my back problems' (later offering me - at 17 - the opportunity to come to his house for a treatment in which I would be naked). When I worked in reception, I never reported all the inane comments made to me by certain managers or sales staff about my abilities or appearance. I have never reported the instances where I have been grabbed in bars or out in the city, or alerted authorities when guys have approached me on trains to harass me and not left me alone when asked. One time late at night, a guy literally chased me down a dark and otherwise empty street to tell me he wasn't going to hurt me (I'll never understand that one).
I realise most of this is not related to STEM, but the point being: this stuff is very much unreported. I wouldn't be surprised in the slightest to hear that 31% is an under-representation of the true state of things. Consider for example that in 2002, 63% of all sexual harassment went unreported. A more recent HuffPost poll found that 70% of people who experienced sexual assault in the workplace did not report it. On college campuses, that number was closer to 90%. It's probably also true that some comments (you mentioned the word slut as an example) are not deemed bad enough to be reported in the first place. I think this is problematic also.
On that note. I do think context is important. If one of my friends called me a slut or similar, I would not be offended in the slightest. My friends know me well enough to know that I am okay with it, and I know them well enough to understand that they would intend it to be taken jokingly and / or with affection. In a workplace with people you interact with primarily on a professional level, I do not think that calling someone a slut, or rating their appearance is in any way appropriate. Perhaps it is minor in comparison to actual physical assault, but I do not see how it is not sexual harassment all the same where the comments are unwanted. Your counter example of insults that you have received, or the claimed under-reporting of assaults committed against men reads like a straw man to me. The fact that we know sexual assault on women to be under-reported makes this:
A rather perplexing statement. Moreover:
Even if I believed the previous statement by you to be true, it proves nothing of the sort. It proves that preconceived expectations of a person's behavior based on gender is a complex and problematic issue for both sexes, which is not really the point of issue here.
I will say that as dire as it might come across, I have not had any issues whee I am currently, and I haven't had nearly as many issues working in labs as I have in hospitality and admin. As CharonY mentioned, biology and chemistry has either an even split or bias towards female participation; particularly at the PhD level, which is what I'm at currently. Five years ago I had just started my last PhD and was in my early-mid 20's; now I am in my late 20's, and half way through my current PhD in the same lab, so I cannot really comment on any differences in that sense.
I have never asked, so I wouldn't know and I wouldn't want to speak for them. Whether or not I'm 'pretty' has zero to do with this argument. I could have the face and body of a rotted potato, it doesn't excuse the harassment, and it doesn't change the statistics already mentioned here.
I find that your argument somewhat misses the larger issue of ingrained sexism, and how that plays out in things like the percentage of women in physics.
Two threads that address these issues very well (CharonY has some great posts in these):
http://www.scienceforums.net/topic/87451-why-is-the-female-crowd-not-attracted-to-stem-fields/
http://www.scienceforums.net/topic/79192-many-women-on-the-site/