Every sexual fact you know is the result of trial and error, with an emphasis on error. For a more scientific approach, and hopefully less slapping, check out Fleshmap
A "data visualization" project from two acclaimed modern artists, Flesh maps titillation levels for over 700 individual body points, as decreed by hundreds of respondents who can apparently afford to be picky as to where people fondle them. Front- and rearview maps show arousal areas on women and men for both touching and being touched; the first rendering, "Skin To Skin", shows the body as a heat map with sensual areas burning bright yellow, giving you the enhanced vision of a sexual Predator. More fun can be had with "Sorting Out Desire", which breaks down real photos into hundreds of tiny boxes, then allows you to scale box sizes according to erotic connotation (resulting in well-endowed, kneeless individuals), or arrange each point in an erogenous-zone grid -- demonstrating that, while women believe their neck to be the most sexy rear point of contact, men prefer their butts in at least nine different places.
For a pop-cultured 2nd opinion, Flesh has visually mapped out body parts according to their frequency in song lyrics, broken down by 11 genres, from Alternative to Jazz. Tip: go with hip-hop, as it's impossible to mess up "Grab yo d*#k!"