Three seashells (Demolition Man, 1993)
Sly Stallone's cryogenically-preserved cop may have to tangle with Wesley Snipes' psychopathic criminal in this sci-fi action comedy – but first he has to learn to cope with life in the year 2032. Specifically, how to use the three seashells that have replaced loo roll in the toilets of the future.
If you're still puzzling over the mechanics all these years later, Stallone himself answered the question in an interview with Ain't it Cool News: "The way it was explained to me by the writer is you hold two seashells like chopsticks, pull gently and scrape what’s left with the third. You asked for it…"