There, I found a very interesting article regarding those terms and the comfortability of using those compared to the actual anatomical name of the body part.
The article points out that the anatomical name of female parts are viewed as obscene 29% of the time whereas male's parts - named anatomically - were perceived obscene 3% of the time. WOW!
It even infers that most people prefer the slang terms over the anatomical medical term.
Also, 1200 synonymous slang terms for vagina!!!??! I'm pretty sure I can only think of a handful!
Anyway- take a look at this paper. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2655816/