I agree with the posters that said that as a bike commuter I would not like to be distracted by trying to hear what someone is shouting out of a car window. There is just too much else to think about while cycle commuting on busy roads.

However, I think your motives were good. I often pass cyclists out there while commuting, either without helmets, or riding on the wrong side of the road, and I do always say something to them about both of these issues. In fact, once I was stopped together with a guy at an intersection, and he responded by asking me where to buy a helmet for a good price, what to look for, etc. He worried it would be too hot, so I was able to explain about air vents, fit, etc.