Maybe it's ok should you have like an extra 6 feet to pass by to not say passing on left . But to not indicate, passing on the left or whatever is as simple as do you have to use turn indicators when passing other cars. Its the law. To me , same principal holds to cyclists. And, I think it's rude not to. I do not alwasys adhere to a totally straight cycling when riding on bike paths. There have been a few close calls since I was not told they were passing.
And I regretted once having spat on a passing cyclist. He was really pizzed. Don't blame him and I regretted it. But, I did not know he was was there. I would not have spit on that person had he said passing on left. Luckily I think I hit him on the leg.Guess, I should have spit to the right. Just thought I was alone.