After a comment below I now want to state first, because I think I was misunderstood, that rape jokes are NEVER OK, regardless of context. However, it does depend on the context how to address them.
Also in general I don't think it is necessary for a group to make such jokes to make someone else uncomfortable, that is why I start with my first clarification. There are different kinds of objectification and "sexual talk" and there are different reasons for them.
So after the update, first I want to clarify something on the general side: women also speak about men as "pieces of meat". It is rather common. If a person find someone attractive but doesn't know them as a person and they are in a group with people with their same sexual orientation, it is very common for them to say sexual things about said other person. That doesn't mean they don't think the other person is not human or anything of the sort, it is just normal human behavior. This of course doesn't mean everyone does it, it goes with personality.
Now a general advice, men (and women really) wouldn't talk (usually) like this if they are aware a member of the other sex is around, because this is not a behavior aimed to make the other person feel bad, it is just goofing around in a "we like sex, we are the same gender/have same sexual orientation, we understand each other" kind of way.
So if you are in a context were there are women around, just tell them in a nice way. Don't say it like "you idiots", say it more like "oops we made a mistake" kind of way.
Hey guys there are ladies around here, let's be quiet or change the
They will probably make some joke about you being such a gentleman or so and actually tone down the conversation.
Clarification: This advice refers to situations when a group of people is talking sexually, in a normal way, and not doing rape jokes or comments of the sort, that as I already said are never ok. I am talking of general sex talk that wouldn't let the other person be comfortable, whether men or women. You can't forbid people talking this way, but you can tell them that there are appropriate places. For instance saying "that woman has nice figure" or "that guy has great abs" is not bad, but you certainly shouldn't be saying things like that, that are meant to be heard by your friends in a way just about anyone, specially of the other gender could hear them. Sometimes people fail to see that, normal sex talk happens in these places, which is inappropriate in the setting but not as a general rule. So if you demonize it and make too harsh a stand, it is actually counterproductive, because it doesn't make them feel they are wrong, they feel like you are overreacting and decide you are just oversensitive. I have seen this happen a lot, so the way you proceed in these situations should depend on what it's being said. And sometimes just pointing out there are women (or men if it is the other way around) is enough.
How do I know this works? Because I have seen it working a gazillion times. Take into consideration that people usually don't want to be embarrassed in public or be seen as awful by people they don't know. So they would be actually thankful that you made them notice that they are messing up.
Now more detailed advice:
If they are just goofing around, the above should be enough, and as I said it is just natural behavior and to be somewhat expected with many people of the same gender/sexual preference together in the same place with drinks. However, as someone in your twitter link said, rape jokes are never ok.
So what to do if someone goes really overboard and makes rape jokes or something else extremely rude? You can either show your discomfort in an honest way or in a joking way, it will depend on the situation, and how you see it. If you are natural and don't try to act like the righteousness protector it should be fine.
Key to this is to not be judgmental: don't make comments about the person, their family or whatever. Sometimes, people are just really lousy at making jokes and get very overboard, but they are not bad, so you can say something like:
Hey dude that's not cool!
Hey don't go around giving people bad ideas! She is a brilliant professional and you shouldn't be talking about her like that.
Friend name here, sorry but that makes me a bit uncomfortable, I
mean she is hot, but she deserves respect, she was brilliant in the
conference, so lets tone down the jokes please.
Some of these options may make you sound a tad more serious than you may feel comfortable with, but if they are joking they wont take it wrong. They will probably just joke about your "seriousness" and move on. You might even be surprised by some of them agreeing with you. It is amazing how many times people actually feel uncomfortable about these kind of jokes but don't say anything because they are embarrassed to do so, they want to look "cool", be "a part of the pack".
The key here is that they are just joking and being silly and they are not truly mean, so you shouldn't linger in the topic. "Nagging" about it won't do anything for your cause, it will just make you look like annoying. If you express yourself clearly without being mean/rude or judgmental (like saying what an awful person they are for saying such things) they will actually respect you and see you as a person that speaks out when necessary.
Now if they are actually being mean, well you have to consider why are they being mean. Is it that they feel threatened by her? Or is just that they are not used to work with women and they feel she think she is better than them? When an outsider comes and is really good, even better than other people of the group, people sometimes feel like the outsider is being standoffish or arrogant, when it is just them not understanding the outsider. Why do I say outsider? In a field dominated by a gender, a member of the other gender is an outsider.
It could also just be that they are plain chauvinistic or mere idiots.
- If they behavior comes from feeling threatened, then it is a bit similar to when they are goofing around, they are just being silly. So you should point it out in a non-judgmental way. Say "please let's not talk about a colleague like that" and of course saying that it makes you uncomfortable would help too. You can mention some good points about the other person, topics of the conference, or how clear she was or whatever positive thing. If they feel threatened, it is their problem and you can't fix that, but you can certainly make them see it is not cool to talk like that, and then move on.
- If they think she is arrogant and that is why they are being nasty about her, the question is: was she really arrogant? Was she really nasty in some way? Well in that case you could agree with them that she is nasty but that is no way to talk about anyone anyway, NOT COOL, and why would they even want to be with a woman they find nasty in the first place? That is just crazy. So you can say something "What the heck dude, I know she wasn't nice but that is no way to talk about anyone! And also, maybe her bad behavior came from having a bad day, and god knows we all have had one of those! Remember when I -here some experience you had or one of them-?". And then joke around a different topic. If she on the contrary was a delight, well just tell them "wooow what just happened? when was she anything but nice? -here you can give some examples-" and then close it saying the same as pointed out before, or that it makes you uncomfortable or that this is no way to talk about anyone.
- If they are mere idiots, well just do the same as when they were just goofing around. Say it makes you uncomfortable or whatever, stay in the group a bit more and then just go away. Sadly when someone is being idiotic, sometimes there is nothing you can do. As they say, idiocy doesn't hurt the idiot, it hurts the people around the idiot. The only way to fight idiocy is with literacy, tell them what you think without being judgmental. And then consider, do you want to be around those idiots? Probably not, so walk off after a safe amount of time.
- If they are chauvinistic, it gets tricky. But since rape jokes are never OK, and I think even a chauvinistic person should see that, I would start with that. You could even make a parallel, like "Jason you wouldn't want anyone making such a joke about your daughter". This kind of men see women as less than human, but that doesn't mean they hate them. It is kind of like with a dog: they wouldn't want anyone being nasty with their dog, so they won't be nasty with someone else's dog. Again it is really hard to change a chauvinistic to non-chauvinistic. In general, this is a behavior rooted in childhood, where even sometimes their own mothers told them wrong. So you can start with the basics, making them be nice and respectful towards women and keep their thoughts to themselves. If they are any smart, in the end they will come to respect the women around them because they will see women are just as bright. But you shouldn't let a chauvinistic person ever get away with their chauvinistic remarks. Never be judgmental, but don't let it pass. And try to get allies that think like you, so you are not the only one who says these things. Don't linger on the topics either. This is a problem that requires a lot of time to be solved, and cannot be done in one shot - it requires steady and unrelenting work.
Where do I come from? I am a woman that works in a men-dominated field. I have seen all this, I have seen this behavior and others, and also I have seen many ways to handle these problems. And I can tell you, letting them pass has never worked, in general it just gets worse. So what you should consider is the situation and how to address it. It is not the same if someone is being silly as if that someone is being mean. I have also read many books about human behavior and conflict management and even taken a course here and there.
I hope my comments are of help to you.