First time was in Venezuela...I was young and stupid, and accepted a ride from a guy in town back to the airport to pick up my rental. About half-way there, he pulled over, raised the hood and said I should drive the car because he thought I needed some guided practice on Venezuelan roadways. I didn't really understand why, but I foolishly agreed and hopped in the driver's seat. A little down the road I saw why as we approached a police roadblock. Apparently the guy didn't have a license and thought he could convince the police that I had been driving all along! They asked for my driver's license, and then, having apparently seen the switch, asked why I was driving. I decided to rat the guy out (in Spanish, of course), told them what happened, and they smiled and promptly arrested my "friend" and impounded the car. No money was exchanged, and they thanked me for my cooperation, told me they hoped I wouldn't think they had treated me badly, and hailed me a cab to continue on my way. The cabbie, seeing the guy in cuffs, laughed when I related the story and said "what an idiot."

The second time was in Canada. I was pulled over after being clocked in my US rental car at 129 km/hour in a 100 km/hour zone. I feigned ignorance as to the mile/kilometer conversion rate, and after seeing that my speedometer only had miles and not kilometers listed, the friendly Mountie wrote me a warning and sent me on my way.