I don't know that yelling is the answer, but I have wanted to stop a cyclist going the wrong way/using the wrong lane/not wearing a helmet/not signaling to explain how they can get from Point A to Point B safely - increase their chances of survival, you know?

Sort of a quiet "hey, I'm a cyclist also, nice bike (if applicable). I've found it's safer for us to be in the right side of the lane rather than the left, and since we are considered a "vehicle" we go with the flow of traffic - easier for us to be seen that way. Happy riding!"