You know that someones is Sx-last when they are completely out of youch with their sensuality and when it is weird or even laughable to imagine them having sex, because it seems completely out of context with theses people. Steve J is like this. Do the experience, try to imagin Bill Gates or Larry King or Steve Jobs or Stalin or Ron Paul or Laura Bush having sex, and you'll see that it works.
Sx, at the opposite have an allure wich screams "SEX" always, wich screams "I want sex, I have sex, I need sex", and if you try to imagine them having sex, it's either stimulating or creepy. Do the experience, see Ann Coulter, Adolph Hitler, th ayatollah Khomeiny, Angelina Jolie, Courtney Love, Elvis Presley or Megan Fox and imagine them having sex, try also to imagine my avatar having sex, you, again, will see the result.