I did it to myself by accident when resetting the trip meter after filling the gas tank. Didn't pay any attention to the speedometer, but after a few minutes did a double-take on the odometer and said "Dude! Who put all those miles on my car!" Boy was I mad, and I didn't figure it out until I got home.

 

I used to do that to friends all the time to see who would fall for it.

It's more convincing if there is very little traffic.

 

I have the opposite situation here. I run with KMs/hr. I had this passenger once, see, and when I was slowing down, I changed to mph. This guy was in kind of a hurry to be dropped off to go for his exercise run. He looked over and thought the car was nearly stopped, opened the door and jumped out. Broke both his legs.