OMG this sorta happened to me. Unloading groceries from car, noticed a can of pop missing from 12 pack. Looked all over and thought wtf, it din't just get up and walk away.
So 2 months later, going to work one cold ass morning, and hear what sounds like a big rock loudly crashing through one of my back windows. Scared the FVCK outta me; I stomp on the gas to get the hell away from there (thinking maybe it was a gunshot) as i'm checking my windows for damage. I stop at a gas station and am shocked to see no damage to windows, and nothing unusual in or around the front or back seats. Do a walkaround the outside of car and nothing. I am seriously stupefied.
Two days later, I had my nephew in the back of car and he noticed a glob of what looks like Coke slushy underneath passenger front seat. Apparently the runaway can of Coke lodged under the seat and waited for the perfect time to explode. Unreal, but at least cleanup was much easier than this poor guy's car.