*You will need to do this achievement in multiplayer with weapons enabled with at least 1 other player.
*The host of the multiplayer match will have to Port forward, ports 5127 - 5129 in both UDP and TCP.
*You will have to evade a missile that another player has fired while locked-on to you.
*To get a lock on a target press the >TGT button, then cycle targets with next or previous button till you are on the player you want. Then face them and wait until the red crosshair appears. You must be with in 200 m of the target to lock on.
*Right-shift is default for firing missiles.
*Right-CTRL is default for dropping chafe.
*Once someone has a lock-on you, a warning Klaxon will start, and it will change once a missile has been fired on you.
*Dropping chafe a second or 2 before a missile reaches you should get you the "Evasive" achievement.
*Pulling an evasive manuver while dropping chafe will increase your chance at evading the missile.

That is all I have at the moment, please leave a comment if you have anything to add.
I hope this helps.

Thanks to Sewaz for helping me figure this out!