If someone gives a stupid remark like "thats a big guitar" or "how do you fit that thing under your neck?" You could stop and tell them its a double bass then launch straight into a 10 minute overly enthusiastuc presentation on the double bass it's origins, its purpose, its place in music history and todays world of music. Including hand outs and diagrams. That would shut them up nicely 
(They would probably then go home and tell their friends about how some guy wouldn't shut up about his giant guitar
)

(They would probably then go home and tell their friends about how some guy wouldn't shut up about his giant guitar
)