Drawing the people around you always elicits a certain amount of paranoia. People know you sketch. They know you sketch people. They also know you've glanced at them no fewer than ten times in the past 60 seconds.
Fortunately there are some settings when, no matter how positive they are they're being sketched - they just can't do anything about it. Classes. Ceremonies. Waiting Rooms. They can't leave. Confronting you is awkward. Tada! Sketch subject!