I pretty much agree with ss that its a judgement call and that out of common courticy(sp)you should slow down and not buzz too close by a cyclist or pedestrian(it is similar too some motorists who do the same to cyclists).Like them(ignoring rude motorists) I suggest you simply ignore rude cyclists as your unlikely to change their immature behavior and there is no use in letting it ruin your ride. .On sidewalks or bike paths pedestrians and slower cyclists often clog up the entire lane nesessitating calling out your presence.Here I usu use"coming thru"and let them decide how to move as I find "on your left" startles and confuses most and they instinctively look left and sometimes even move left.Actually though I try to avoid paths and sidewalks and this is one major reason why.