Mostly I avoid any social gathering that is inhabited by the sort of person who would ask, “So what do you do?” But if this question does somehow come up, I have an “IN CASE OF EMERGENCY BREAK GLASS” box inside my head. Inside the box is this sentence: “Oh, I’m going to school for puppeteering.”
I have about four or five believable sentences to expand on this if need be, though typically the word “puppeteering” is potent enough to kill a conversation outright.
I should also mention that when someone says “So what do you do?” I usually have to turn my head to the side and pretend I’m sneezing or coughing so I can roll my eyes really hard (an involuntary response), and then whip back and feed them the puppet stuff until they decide they hate me.
Also if I’m in a really bad mood I just hold up my hand and say, “C’mon. We can do better than this.”