I think a father should instruct his son on "the facts of life" including telling him about the changes in his own body. And if the father and son are comfortable with nudity, it could even include education about masturbation. They shouldn't be touching each other, but as an educational experience I see nothing wrong with them masturbating in each other's presence. I just don't see it as sick at all. That shouldn't be the only focus of it, there should be a lot of general instruction about sex and women and all the details that the son wants to know and needs to know. The son is going to have to find out all this from SOMEONE. I kind of wish my father had done this for me - he never mentioned sex at all to me. I remember the first time I ejaculated, I thought I had done something wrong at first. I just don't see anything wrong with a father and son masturbating together (but not each other) as a sex-ed experience.