Most common: "I didn't know BMW made bikes."
Next most common: "Can you do a wheelie on it??"
I have one guy in my neighborhood who every time I ride past him does a wheelie motion with his hands like he wants me to wheelie the bike. Once he was walking his dog past my house as I pulled up so he asked me, "How come you never do a wheelie for me dude??" I pulled the 12 pack of Sierra Nevada out of the top case and said, "I don't want to break my beers dude!!"