used for registering a (usually minor) coincidence UK From the children’s card game during which players cry “snap!” whenever matching cards are exposed.
NICKY: Where’ve you been? TRICIA: With Daddy. Where’ve you? NICKY: With Mother. Talking about marriage. TRICIA: Snap! NICKY: Don’t use those dreary schoolgirl expressions the whole time, Trish. You’re nineteen now. — Peter Nichols, Promenade[SixGranadaPlays], p. 47, 1959