Closest encounter would be on a 3 lane highway.  Both the right and center lanes, cars are in a staggered formation.  But there is this stupid person clogging the left lane by pacing the center cars.  As I approach him, I blink my highbeams at him.  He notices me and is nice enough to merge over to let me pass, but this guy doesn't even check if he can merge safely to the right.  There's a bunch of honking and brake lights as he cuts off the other driver, but luckily, nothing happen.
So yes, I almost caused an accident by forcing the guy to move out of my way, but he was also an idiot for crusing in the passing lane and not checking his blind spot before merging over.