I did one of these threads a long while back. Anyhow, my two best are:

1. Coming back from a Grateful Dead concert in Wisconsin me and a buddy were smoking a joint in the car, going about 70mph. I look in the rearview mirrow and see someone right on my ass. I look again and only then notice the flashing lights on top of the car. In a total panic we open the windows and, as smoke pours out, we pull over to the side of the road. The cop flys by, off to some other destination. We must have sat their by the side of the road for an hour before we got our shit together and started to drive again.

2. I was living in Shanghai China and had managed to score some hash from these guys who came from the area of China that borders Afghanistan. I found a nice little secluded spot in a local park, pulled out my pipe, and started to smoke my hash when I realized a cop had quietly walked up and was standing beside me. I figured I'd probably spend the rest of my life in some hellish Chinese prison but the guy just stood there. After a few minutes he asks me where I'm from so I tell him the U.S.. Now that he realizes I can speak Chinese he just starts rambling about all kinds of shit.

Next thing I know there are like 10 people just standing there watching us. I'm totally tripping out when I begin to realize the guy really has no idea that I'm smoking somehting illegal. Weed is pretty rare there so its not like here where every cop would know immediately. I was just a strange foriegner doing some strange foriegn thing. I looked at my watch, made some comment about having to be somewhere and split.