Citadel General Assurance Co. v. Vytlingam, 2007 SCC 46
Click here [3] to link to the full judgment. 
(Insurance / Automobile Insurance)
While V was driving through the U.S., someone dropped a rock from a highway overpass onto his vehicle, causing V extensive injuries.  The assailants were convicted in the U.S., but one was inadequately insured to cover civil damages.  V claimed compensation from their Ontario insurer, arguing that the assailant was similar to an inadequately insured motorist.  Although the assailant had used a truck to transport the rocks to the overpass, the Court dismissed the claim, finding that dropping the rocks broke the causal chain and any connection to the truck.
Majority/dissent: 9/0