"Was your trip business or pleasure?": "Is there a difference?" (with a smile, or a sarcastic sigh).
"Do you know why I pulled you over?": "My friend was once pulled over and thanked for properly signaling!" (big "i'm clearly joking" smile).
"Do you have anything you'd like to tell me?": "My mom always used to ask that a lot... usually when I was in trouble. Am I in trouble?" (smiling! always smiling!)
This usually gets them talking back in a joking manner... or get straight to the point. Either way, you've established that you're smart and friendly, not a smart-ass. When they do get to the point, you can usually clearly state (with a smile!) "I'm afraid a lawyer friend once told me not to answer these questions when pulled over."
You might get some special attention, but you probably won't be put in the naughty corner and told to "cool down".
/me activates qik on Android
/me tagging qik stream with #copwatch
/me looking both ways, leaning forward, stage whisper
I could use a blowjob