I've heard of this idea before and it sounds great. But I can think of a hack for it that could make the trip even worse.

"This is a coin. It's just a regular coin from my pocket, but I want you to carry, and know that as long as you carry this coin - for the rest of the night - you'll be safe."

(lean in close to whisper into the recipient's ear)

"But if you lose the coin...if you lose the coin, you're doomed, mate. Completely f*cking doomed."