That's funny. I'm ususally quite firm about insisting on seatbelts all around before driving away. However, once I didn't check when I drove to lunch with some coworkers. We went over a old one-lane bridge in both directions. It was one of those steep, tiny bridges:
/-\

Anyway, I was driving my old beater Subaru wagon and there was no traffic so rather than crawling over it I took it at about 35mph and caught, ahem, a bit of air on the far side. Imagine my surprise to see the two dorks in the back bounce off the roof of the car in my rearview mirror. Imagine how they carried on. They also scrambled for their seatbelts pretty fast.

Yeah, they blurted out a few choice things.