Opening weekend, 1999 the day before the newspapers published their weekend reviews. I and the rest of the audience went in blind.

Whilst I twigged a little earlier than most when the ring hit the floor, the audible gasp across ther cinema as everybody realised the twist was one of the greatest moments I have ever experienced at the cinema.

The closest I can think of in recent times was in Avengers Endgame during the Soul Stone retrieval. Nobody expected that one.