It works exactly the same as negative experience boosting. People would quit out of hundreds of games to get a ton of losses, which then, when partied up with their friends would result in them levelling quickly (1-50 in around 20-30 games).
Bungie caught on to that and started handing out bans to those who quit out of too many games in succession, so people have started deranking as a work around. Usually it's done with a turbo controller, anyone who actually sits there losing is a complete nerd.