There are incidents that require a warning yell out –rider! riders coming!, etc.- and, if you don’t have a bell mounted, a simple technique is to change gears when approaching the rider/person; the switching of the gears are typically heard. Stay away from yelling out left/right because it does at times confuse folks. If its safe to pass without warning its safe to pass. Be cautious.
Typically the only time to slow down is if you want the other rider(s) on your wheel. The other rider’s pace should not dictate your pace; focus on your pace.
Headphones… sometimes focusing on the ride, listening to the wind, and birds, or saying hello to people is the purpose of the ride; and other times music helps stimulate the workout, helps tune down the traffic noise, and if there is a good ballgame on I may tune in. It depends on the purpose of the ride, the surroundings, and the mood.
If headphones are illegal, are deaf people allowed to ride bikes?