Things that I had never done until today:
Dial 911.
I was driving my friend Migdalia to the grocery store and we got stuck behind this car on Rt. 10 going 15-20 mph in a 35-40 zone. I grumbled but was okay driving behind them even at a snail's crawl, but then the car started wavering back and forth across the narrow lane, so I got on the car and called 911 because I didn't know the number for the local police and reported them as I saw them turn off onto a residential lane.
It felt a little weird, as I've never called the cops on someone, especially for a traffic thing, but the way they were jerking around the lane convinced me that it was better to be cautious about the whole thing. Migs agreed with me. 911 dispatch put me through to the local police dispatch, and we had a quick 3-way where I described the car, what they were doing, where they'd turned off, what I remembered of their license plate number, etc. They called me back later while we were shopping to let me know that they'd found the person driving, there were no signs of impairment, and that the driver and his wife claimed to be unawares that there was a minimum speed-limit and that they'd been driving home. I think they might have been an elderly couple, but I didn't catch a look at them.
At least people arrived safely to where they were getting, but given how quickly traffic stacked up behind them and how closely we were all crammed together for the quarter mile we were stuck behind these guys, had the weather been rainy like its been almost all of this summer there could have very easily been an accident.