They say a little knowledge goes a long way. Think of some ways or situations you might know more about somebody. Either somebody you know, or a stranger. Perhaps even a group of strangers.
The knowledge doesnt need to be correct, or even real. Job interviews, seeing somebody when they don't see you (maybe on a date, when they're actually married?), having just heard the latest gossip about them from a friend or family member, even having overheard something about them medically, which they don't realize you know. Taken a step further, pehaps what you know comes from a dream, or maybe a sign you interpret in a certain way. So many possibilities where we know something, or think we know something about other people.
Explore the way this knowledge might affect a meeting between you. The tension, or assumptions taking place. The way you might judge, or re-assess a person or jump to conclusions without them knowing. Write your piece and explore the rough areas this might cause.
Check out Barbara Hamby's Ode to Untoward Dreams on her website.