Here is an easy way to get this: Start a split screen race with a second player that you control and put the race mode to magnetic mayhem. When it come to ship selection choose whatever one you want for yourself but for player two select a ship that has low defense. Then start the race. Seeing as its Magnetic Mayhem just keep firing at the second player (because you can't move two different racers at one time) and keep attaching the magnets to player two. Keep doing this until he blows up and then the achievement should pop up.