It's every danged time I ride my bike. Or run on a crowded course. Some people get road rage in their car. I get it in my Mizunos. Pretty much the same, yes? ;-)
Rule #1. Let's start with the golden rule of running. Or riding the escalator, for that matter. Or generally functioning in society. Unless you're in the UK:
STAY TO THE RIGHT!!!!!!
Not the middle. Not the left. On a bike, it's dangerous not to follow this rule. On a run, it's also dangerous because you might get hit by a bike. And in a race, if you're stopping and not on the right, you're just ticking everyone else off.
Rule #2. Your corral is your friend. Stay in it. No one cares if you started first. Only thing that matters is if you finish first (unless you're an elite so I've heard). Plus, it's demoralizing to get passed for the first couple miles so you may as well start with people close to your speed.
Rule #3. Run MAX two abreast. Just one if you're really fat.
*Credit OUAL for this one.
Rule #4. Walking 5 tiny dogs on a busy path? Cool, but keep the dogs on a close leash.
Rule #5. Teach kids basic running / biking etiquette. There is nothing scarier than almost running into a 5 year old trying to learn how to ride a bike and swerving all over the dang place.
Neighborhoods > Really Busy Bike Paths.
Rule #6. Yer Gu. No one wants to step in it. So no throwing it where other people are running. If you're racing and need to throw it on the ground, throw it away from the path.
Rule #7. I know giant packs of bikers are annoying but they have a right to be on the path / road. Big Packs of Bikers: Try to be as unannoying as possible and stay to the right.
Rule #8. Warn People if you're passing on your bike. Yelling "On Your Left" or "Good Morning" is all ya need.
Rule #9. I believe Lauren mentioned this previously, and I have never actually witnessed this in real life, but for God's sake, Don't Cross The Finish Line Twice.
I know I'm missing some rules (and may be entirely unaware of some) so anything to add?