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.
Take a look at the world and all the shitty stuff happening every single day again. Then, think about a joke referencing a penis.
Do you really feel the need to be offended? Do you really think it is worth to tell the world someone touched a broken braincell in your head because of a penis joke? Clearly, you have your priorities wrong miss Richards. Same goes for the company firing the guy, why would you care about a crazy woman with penis issues?