I'm 21 and regularly freak out at people not properly strapping in a carseat.

That being said... SERIOUSLY!? NO ONE said anything to Prince William or Kate? I'm sorry, but after loosing his mother in a car accident caused by the paparazzi you would think he'd be more informed on how to keep his son safe in a car. DH is obsessed with keeping our girls safe because his brother died in a car accident. General rules of our car:

EVERYONE wears their seatbelt. No ifs, ands, or buts. I don't care if we are going across country or across the parking lot.
Anyone under 12 years old has to ride in the back seat.
Anyone under 8 years old or 4' 8" has to be in a booster seat
Anyone under 4 has to be in a 5 point harness booster seat
Anyone under 18 months has to in a rear facing carseat (We prefer until 2 years, but SD out grew the rear facing safety requirements for her carseat at 18 months)

Carseat straps must be "unpinchable" meaning they are tight enough that they can't be pinched. The chest piece must be at armpit level. The carseat must not move at the base. I've flat out climbed into the kids carseats to make them tight enough. I'm 5'10, 200 lbs (Just had a baby, give me a few weeks ) and drive a Toyota Camry. There is NOT a lot of room for me to get into a carseat, so if I can manage it just about anyone can!
There are no excuses. Children can turn into tiny torpedoes if they aren't strapped in properly. A baby turned around to early can be killed by internal decapitation. A baby with the chest piece too low can suffer massive internal bleeding. I love my girls way too much to ever let something like that happen to them!