When does your muse strike?
For me it's in the shower or during a walk I've taken many times before. But that's just me. For me it has to be some kind of repetitive activity that requires almost no thought, and that's when I get many of my ideas for plots or details for stories. Not all of the time, naturally. But if I get famous and have to write for a living, I'll most likely be the cleanest author the world has ever known.
Stevenson got his idea for Dr. Jekyll and Mister Hyde after waking from a bad dream. So when does your muse strike? What does it take? A bottle of cheap wine? An expensive doobie of Purple Kush the size of the Hindenburg? Sixteen cups of coffee?
Tell us where or when you get your best ideas, and fear not, your modus operandi will remain secret. (sure, why not, it's all over the world on the internet)