Most cyclists (not all) don't seem to get it.

Anything more complicated than "passing" is too much to process in a split second. If one considers the closing speed to a pedestrian, yelling is required to be heard at the distance you must announce your arrival. If you're close enough to be heard in a normal voice, you don't give the other person time to react and you time to stop in the distance left. Most cyclists do not seem to understand human reaction time, stopping distance, and speed at all.
According to an on line converter 10 mph is equal to 14.6 feet per second. To allow someone to react and know what to do, and for you to stop your bike is about 2 seconds (approx) If you say passing at 14 feet away you already have no time to stop safely if they go the wrong way. You really need to be about 30 feet away at only 10 mph at this distance you need to yell. I don't see any other cyclists doing this. Many say quietly when right beside me "passing on your left". At that time the announcement does no good. At that distance just pass.
At 15 mph you will go 22 feet in one second. Do you give 22 feet of distance and yell, when going that speed? Then plan for an impact. The overtaking vehicle is always the one responsible to avoid a collision. I rarely see a cyclist do this safely. Most drivers do not get this either, they mostly tailgate. If there is a panic stop from the car in front they must hit them very hard.
The closing speed and cyclists perception of time is what the biggest problem is.

There is only one person you can count on, that's YOU, not another person. Yes there are lots of idiots around, yes it can be annoying. Don't give them a chance to hurt you. It's safer and less stressful if you take control by allowing time for others to do the wrong thing.

Don't expect others to do something for you in one second. On an mup or a bike path you need to go slow, that what all the rules say anyway. They are not wrong.
This is a good reason to ride on the road. Drivers, peds, other cyclists will be more likely to expect something coming faster. Of course there are always those who don't. But it's more likely. It's up to you to ride where you want. It's up to you to pass peds safely.

Of course yelling "Passing!" instantly followed by a loud "WOOF WOOF" and "DING DONG" simultaneously either gets results, or cardiac arrest. Hopefull they fall to the right when they die.