To add to what Batmom said in her first post, dogs are very situational. You might, for example, teach your dog to 'down' in the living room, and be unable to get the same behaviour in the yard.
Outside, people have more room to approach, probably looming and staring and maybe chattering. If you know the person, you could ask them to avoid eye contact and approach slowly quietly and sort of sideways (side-on instead of head-on) with hands dangling at their sides rather than reaching.