What is it?
This is a dick move perpetrated by cyclists while on shared bike/pedestrian paths (or worse, on footpaths).
Essentially, it involves not warning pedestrians up ahead that you’re approaching.
In most cases I assume it’s because the cyclist (and I am an occasional cyclist) doesn’t want to ring their (to their mind) lame-sounding bell and draw attention to themselves. Additionally, it could be because the bike doesn’t have a bell (get one!) or because they think they’re going slowly enough that it won’t matter (you’re probably wrong) or some other stupid reason.
Why is it a dick move?
Because people are hard to predict and they may pull out an umbrella, point at something, step off-line to pick a flower, pick up some litter, stop suddenly to look at something or some other action that you (as the cyclist) didn’t anticipate.
This would result in you hitting or clipping the pedestrian… which is bad news for both of you.
It’s so easy to do – just ring the goddamn bell!
However
Some pedestrians make it hard by wearing headphones and playing music so loud or wearing noise-cancelling headphones so they wouldn’t hear you anyway.
For them, you should definitely give a warning (as you would for everyone else) and hope they can walk a straight line. Being a pedestrian on a shared path but unable to hear approaching cyclists is an associated dick move.