I was in a triathlon once, and during the biking portion witnessed the following incident. We were going uphill and a guy who was going faster wanted to pass a slower rider. The slower rider was far out into the road, so the faster rider had to pass him on the right. They almost collided and then started yelling at each other:
Slow Rider: Pass on the left!!
Fast Rider: Stay to the right!!
I was with the faster rider. So who was in the right? (Or were they both wrong?)