Dodge This! is a Halo 4 achievement added with the Castle Map Pack. It is awarded when the player, in Castle DLC matchmaking, gets 2 Spartan Laser kills with direct hits in one match. Killing an enemy with splash damage does not count toward unlocking the achievement. It is represented by a number 2 in the center of a Splaser Kill medal.
The name of the achievement is likely a reference to a quote from the film The Matrix.