When you are done masturbating, the white creamy substance that comes out of the male genital (caused by fapping) that could be constituted to cover a popular Starbucks Coffee.
To suffer from fappathy is to have such a low libido that not even masturbation seems appealing. It's an amalgamation of the word Fapp (To furiously masturbate) and Apathy (A lack of enthusiasm or concern)