I think you miss my point. Where I come from, nobody - and that can be taken very literally - will be offended by a joke about penises between to friends. Why not? Because it is not something to be offended about. There is a lot of crap happening in the world today and jokes about penises is not one of them. That's all there is to it. If you do make this a big priority in your live, and even feel offended by it, your brain is kind of broken. Like when you believe in God and thus think it's OK to murder others that don't follow your beliefs. That's a broken brain symptom.

So it's not so much about drawing a line as there should be no need to draw it.

It's a bit - in a far fetched way - like the song Tim Minchin sang about the pope: http://www.youtube.com/watch?v=Sph8Qu8wLAk