... when you speed up on the freeway to catch the semi truck for a draft.
... when you look at the wheel wells of trucks and picture them skirted.
... when you sneak over to the gas pump of a Prius driver to see how many gallons he.she filled up after they left the gas station. (If only I knew the miles they put on that tank!)
... when you reconsider answering "No it's not a hybrid, just gas." when in reality you know it's a gas/gravity hybrid.
... when you estimate how many mpgs less a vehicle is getting when you pass them on the freeway. (With a big grin on your face!)
... when you peruse the interwebs desperately searching for your car's exact frontal area and your tires' rolling resistance.
... when you can't wait to post a question/idea/result thread to EM because no one in your physical vicinity would be interested in such information.