I think that one of the major issues facing conferences is the distinction between professionalism and private life. The way one behaves with good friends is very distinct from how one behaves in a group of strangers, which is distinct from how one behaves with your co-workers or other professional relationships. I think that the mixed culture of a conference might exacerbate this problem: despite the fact that you're attending with friends, and perhaps even going out for drinks, it's not the same as being in a solely social setting.
If I'm with my friends, I know what jokes are appropriate, and which ones aren't - I've had the experience to do that. On the other hand, if I'm at a conference, someone nearby could have a bad reaction to a comment that my friends wouldn't react to - people are different, and an "innocent dick joke" to a friend could really bother someone else.
I don't pretend to say that this is the sole problem, or even a real solution, but I think it might be worth recognizing.