Killed 10 ejecting Pilots.

When an enemy titan goes into its "doomed" state, the Pilot can manually, or with a certain loadout automatically eject from the cockpit and fly into the air. When you see this happen, look up and take careful aim to try and kill the Pilot before he lands. The Chain-gun and Arc Cannon on the Titan or Carbine with a Pilot will be your best bet for this achievement as the other weapons are much slower to fire.

If you happen to be Rodeo-ing the Titan when its Pilot ejects, you will also be thrown into the air at the exact same speed. Flying side-by-side, it will be easy for you (or him) to get a kill, especially locking on with the Smart Pistol.