I just say I'm a web designer or web developer. Usually, people hear that and don't follow up with more questions since it seems self explanatory.
This is the one I usually use as well. Sometimes it comes with a follow up question like: "how much do you charge" (to which I make up an absurdly large dollar figure) or "what's one of your websites?" (to which I point them to one of my more known websites that don't have adsense on them)