Fap meets appetizer. When fapping (masturbating), a fappetizer is something, usually porn, that you fap over a little to get in the mood and build up your appetite for the main course, which will be whatever you finally ejaculate to. Word coined by Little Lord WTF? (WTFSexFacts)
Little Lord WTF?: "I fapped off to it a little. It was a fappetizer. The porn film I watched afterwards was the main course that satisfied my hunger."