You know, that is a great question! Unfortunately, you can’t legitimately have another player’s car impounded in GTA V—but that shouldn’t stop you from trying. We’d suggest stealing the other player’s car and driving it to the impound—you know, maybe even crash it through the fence into the impound yard—then leave it there for them to figure out how to fetch.
At the end of the day, this strategy results in the player’s car being in the impound, right?