The oddly-named "Open Source Boob Project" has generated a whole lot of internet dander. Since I was neither an attendee nor involved with the event in any way, I'm not going to make any attempt at judgement on the events that transpired; others have done that in spades already.
What I will say is that I will agree that in any given public setting, be it a mall, a convention, a workplace, a church, or what have you, nobody should expect to have to wear an indication that they don't want to be placed in an uncomfortable situation by the actions of another. That should be the norm.
That is not a clear definition. It's horrendously nebulous, because what makes Betty uncomfortable may not be the same thing that makes Charlene uncomfortable, and what makes Andy uncomfortable may not be the same thing that makes Dave uncomfortable.
Some things have been codified by law. I have reasonable expectation that I won't be inexplicably groped by another person, that I won't get socked in the face just because "I needed a good sock in the face" (except in come parts of Texas where it's a legal defense), and that I won't get my belongings taken from me by force or coercion.
But there are other areas that aren't codified. If someone makes eye contact and smiles and says hello, that may make me uncomfortable. That's not something that I have protection from under the law, and it's not something that I have a reasonable expectation of protection from. If that person tries to continue a conversation, it might make me even more uncomfortable. If that person asks me for money, it could cross the line into panhandling, and in many places there are legal protections against that.
At the same time, when I'm out walking the dog, I will very often smile and say hello to people I pass by. I can tell that it makes some of them uncomfortable, but I still do it to pretty much everyone. And quite often if it's somebody walking their own dog, I'll ask if the dogs can say hello. More often than not the answer is yes, and there are a few moments of brief conversation. A few times I've been rebuffed where I got the distinct impression that the woman (and it's always been women) did not want any interaction with me, and it had nothing to do with the dogs. I don't take it personally, as I understand that there are some women who might find me intimidating or offensive or distasteful or some other adjective that makes them not want to deal with me, and that it's nothing against me personally-- it could be all men, or people in general, or guys with glasses, or people who smell like wet monkeys sprinkled with cinnamon and nutmeg.
Then there's my behavior when I see what I consider to be an attractive woman wearing jogging shorts with something printed across the butt. I check out her ass. Shocking, I know, a supposedly enlightened man checking out a woman's ass and objectifying her simply because her body satisfies my straight-white-male aesthetic without having any sense of her personality or her mind. How dare I!
(Wait, is that sarcasm I hear drip-drip-dripping over in that dimly lit corner?)
Here's where the concept of social context comes in. If the entirety of my social interaction with you is seeing you (and your fine fine ass) on the sidewalk, then I have no social context for anything else about you other than the way you look, and that you jog. I'm not making a value judgement about you as a person, I'm making a contextual judgement about one facet of you that exists in this instance.
If I later run into you at a friend's party and get to having a conversation with you where it turns out that you're really nice and smart and have a thing for bad horror movies and we get involved in an hour-long conversation on the storytelling merits of the zombies in the Romero "Living Dead" movies, I have much more of a social context for your intellect and personality and interests, and I'm going to make a more in-depth judgement of your attractiveness to me. It's still a social context, and a judgement within that context, but it has more depth to it, more substance.
If I then express to you that I've enjoyed this time that I've spent with you and would like to get together a different time to talk more and maybe expose you to Frankenstein Reborn and Special Dead, and you have that shadow cross your face and tell me something to the effect that you only date men that you actually find attractive, you are making a judgement about me based on that social context. It's a different set of judgements because you're a different person than I am, but it's still just as valid as mine.
And when I keep walking by your house late at night, it's just coincidence that you happen to live on my dog-walking route. Yes it's quite long, I need the exercise. And the camera with the telephoto lens is coincidence as well, I just happen to like taking pictures of architecture because I'm remodeling my house and I like getting ideas for possible architectural details from houses in the neighborhood, and it's just coincidence that I happen to like the architectural detail around your bedroom window. And I often take several pictures to capture various aspects of the detail in different lighting conditions; it really wasn't necessary for you to take out that restraining order.
So back to the matter at hand: Is it a reasonable expectation that when you're in a public place that you won't have someone you don't know walk up to you and ask to touch your breasts (or your butt, or your nutsack, or what have you)? Yeah, I think that's a reasonable expectation, even at a con where many social fringes are present. However, if you're at a private party where it's made clear that this is expected behavior and you have the option to not participate, and you can make your willingness to not participate made clear by wearing a button, then it seems like wearing the button would be a reasonable course of action. What makes it so is the clear delineation of boundaries, the drawing of a line that says "this is acceptable behavior here, but not beyond this line".
I am reminded of an event from my younger days, a party that had "groping booths". These were rectangular booths that were set up on the floor, really just a simple framework of wood that was wrapped with an opaque cloth; the cloth had holes in it where you could put your hands and grope the person inside the booth without ever seeing them. The person inside the booth was a volunteer, and your participation was entirely voluntary. It was inherently sexual in nature, purposefully so, but consider that you new neither the identity of the person inside the booth nor their gender. You could get a real surprise when you stuck your hand in.
There are those who are seriously squicked out by the idea and are right now reaching for the hand sanitizer. There are those who are offended by the very concept that such a thing exists. There are those who are both somewhat squicked and a little turned on. And there are those who are drawing up plans for their very own groping booth in their heads.
But for just a moment, remove yourself from the squickness and consider the Skinner Box psychology of it. It's a beautiful concept in social programming.
And there is a perverse part of me that wants to set up a booth similar to this with a sign that says "inside this box is a beautiful naked woman who wants you to fondle her breasts", but at random times have either:
1.) a woman who is willing to have her breasts fondled by strangers (i.e. positive reinforcement)
3.) a set of rat traps (i.e. negative reinforcement)
This would probably be a good time to take me off of your convention room party planning list.