I can never find the original post, but someone here on BF has the greatest pwnage response to "You're not a car" ever. It went something like this:
Stopped at a gas station, driver filling tank looks over at cyclist and says, "You're not a car, you know."
"You're right, I'm a motorcycle."
<Driver looks at bicycle disdainfully>"Where's your engine?"
"You're talking to it."