First, if it's just a stupid joke among peers, you can have a conversation with those involved about appropriate language and respect. Tell them it's not okay to use such vulgar terms in relation to your son.
Well, without more context, it's hard to say exactly. It could be that there is some sort of object or situation that has been misnamed or misrepresented as a 'huge cock'. Maybe your son has a large - sized item that someone is joking about in a very improper way. But we should always be cautious of using such vulgar language when referring to children.
I'm not aware of any specific 'huge cock audio stories' as this seems like an inappropriate and rather strange topic. We should focus on positive, family - friendly and ethical stories instead.
In the animal kingdom, male deer grow large antlers. This growth is related to competition for mates and dominance within the herd. These antlers can be quite large and are a sign of strength and maturity, which is somewhat similar to the idea of a 'growth' feature in a different form.
Rather than such improper topics, we could talk about stories of young guys in volunteer work. There are many young people who are devoting themselves to helping others in poor areas or in environmental protection projects. These stories are inspiring and can set good examples for others.