You criticize what the person did and state you reasons. You avoid making allusions on sterile cyclists if that person happens to cycle to work.

It is easier to criticize people if you did not picked up on them nor mocked nor humiliated them previously. Because a.) they will have more trust to what you say b.) they will not assume you are not just humiliating them again c.) they will not be predispose to see you as a jerk.