I'd like to stem a couple of obvious, but inevitable (for HN and some other tech communities) criticisms that are bound to appear:
1) Yes, this stuff is tasteless and offends the sensibilities of most decent adults. (Invariably, someone likes to point out that it offends everyone, and conclude therefore that it can't be misogynistic)
2) Yes, people differ in their tolerances for crudeness in their humor. First, I think most people can agree that none of this was actually even funny -- as in, these presentations did not successfully execute the elements of humor. Second, a hackathon is not the place to get up on stage and pretend to come on the audience. There's audacity -- which, when coupled with other necessary elements can make for a great presentation -- and there's poor taste.
3) Yes, some women will take particular offense to these presentations and they are justified.
Allowing a couple of dumbasses to get up and laugh about staring at breasts and dropping terrible puns -- even when their presentation is self-deprecating and they hint that they know how crass they are being -- sends the message that the organizers and the audience accept the premise of the presentation: that leering at women's bodies in a completely unaware manner, is acceptable. It's not -- please let there be nobody who contests that point.
(Aside: a woman in a low-cut shirt is not putting her breasts on display for public consumption. And leering is different than looking -- nobody is saying that you aren't allowed to notice the attractiveness of a woman.)
Getting up and pretending to inseminate the audience is just gross, and as an act, it is at the same level as the guy in my seventh grade class who drew a full-page phallus in my yearbook. His excuse is that he was thirteen, and assumed that everyone else was as obsessed with his genitals as he was. That people are laughing about this sends another message, and I can understand if women are more sensitive to that message than men -- who were themselves thirteen y/o males at one time.
I don't know if I've demonstrated why things like this create an environment where it's hard to say, seriously, that women should get into tech.