Grammy Jewels -- Delivery Guy Lost $15 Million ... Chopard Sues

One unlucky Grammy celeb was supposed to get draped in $15 million worth of Chopard jewelry -- but got stiffed when a delivery guy went rogue and lost all the loot ... according to a new lawsuit.

The Swiss watchmaker and jewelry company says it hired Ferrari Express, Inc. -- no relation to the sports cars -- to transport and safeguard the merchandise back in February ... on the night before the Grammys.

According to the lawsuit, Ferrari's guy decided to take a very costly detour. Chopard says he allegedly brought the van home and parked it on the street -- WITH $15 MILLION in jewels still inside -- in a neighborhood where "vehicle thefts are common."

Genius.

Naturally, the van and all its contents were gone in the morning. Chopard says Ferrari Express refuses to pay up, so it's suing for the $15 million and then some.