Rule34

For anyone too lazy to write their own porn, describe anything and Rule34 will make a porn version of it. It can be anything from a single word or two to a full-blown description of your favorite scene of fiction; it will be turned into porn. If you don't see porn in the first response, type 'continue' in the prompt, and the scene will eventually have porn in it. Or just enter prompts to guide the scene to where you want it to go sooner.