Today a stranger asked “Don’t I know you?”, which happens all the time; I must have a generic face — but it seemed especially funny after watching a lot of Buffy the Vampire Slayer, in which anyone with a speaking part is likely to be Not What They Seem. This bit, at the end of the second season, came to mind:
Joyce: Have we met before?
Spike, politely: You hit me with an axe once.