The easiest way to get this achievement is by going to the game mode PIG VS 100, and literally just spinning the
like mad, you can even get creative like I did and mash
, it helps with other achievements as well. I was getting around 50 kills every 2 or 3 minutes using just the left joystick method and around 70 every 3 or 4 minutes using the button mashing method.
PIG VS 100 has twice the amount of enemies that CLASSIC mode has, and makes this achievement a breeze but also wears your thumbs/fingers out really quick. I would also recommend this strategy for the Rocket Bender and BeckHAM achievement.
Hopes this helps! Happy achievement hunting!