I don't know where you heard that from. I don't think the balls are a way of identifying a sexual partner. I think it's a tuff thing
Maybe that's what he was hoping it was for. Lol
Well since you both insist on knowing & must be interested in having them this is where I read that from, here is the link. As I stated urban dictionary....Google it!
http://www.urbandictionary.com/define.php?term=truck nuts