Everyone in the (car)pool!

In my ongoing quest to do my part (and save some gas money), I started carpooling to work. I haven't been in a carpool since Kathleen Robbins' mom used to drive me to cheerleading practice. It's different as an adult.

I frequently work with my fellow carpooler and we have a good relationship, so we have plenty to talk about on the ride in (at least today), but I feel like we should have a "no talking shop in the car" rule.

But it's weird being in someone else's car (or even commuting with someone else in your car). Do I have to drive safer? Is it okay to openly vent my spleen at my fellow motorists (in a strictly metaphorical sense)? Can I talk back to the radio, as I am prone to do? Have I just given up two precious hours of "me time"?