It is not just Toriyama, but the Japanese in general that have a strange sense of humor that is quite out there and sickening to western readers, or viewers.

I read the manga and i understand the joke set up. it is a pretty jevenile joke. Goku realizes that Bulma does not have the same as him down there,lol when he sees her naked or something i'm trying to remember since it has been years since i read the manga. He was also surprised she did not have a monkey tale like he did as he thought that was normal and everybody had one.

Then again i am not sure if these were the real jokes since i cannot read japanese and this is only based on half remembered stuff from the viz translation.