Maybe Next Time Buddy
From Halopedia, the Halo wiki
Maybe Next Time Buddy is a Halo 3 Multiplayer achievement. It is awarded for boarding the same vehicle you've been thrown off of within ten seconds in any free for all playlist. The achievement awards the player 5 Gamerpoints.
It is represented by a red octagon with a hand making a "stop" sign.
This achievement's icon is identical to the emblem entitled "Halt."
A way to do this with the Banshee is to do an upwards barrel roll as you are being boarded. If timed right, you will be flipped upward as soon as you are ejected, and you can come right back down on the Banshee to re-board it.
The vehicle must still have the hijacker in it; if you kill them and then board the vehicle, the achievement does not count.
Another way to unlock this achievement is to get the ghost on snowbound and drive it into the underground section where the shotgun is. Simply wait for someone to get up to the ghost and highjack it, and since there is not much room for the highjacker to move, you can very easily highjack the ghost back without the enemy getting away.
If you are in a large vecinity when you are highjacked (eg. High ground, Isolation), shoot an over-charged plasma pistol shot at the ghost, as this will "pistol whip" the vehicle and stun it for 3-5 seconds. However trying the method above is an easier way to unlock this achievement.
The match does not have to be ranked, so it's possible to get a friend, go to Rumble Pit, and get the achievment there.
Related Links
