Many players so far, have experienced difficulties understanding what to do or how to do the achievement "Adrenaline Junkie". The Achievement itself is tough, as it is near-to impossible to do. This achievement can only be done in single player.
The achievement is not explained well, and you'll probably have yourself parachuting left right and center and body slamming the ground in a kamikaze frefall attempting to do what it asks, however, this is what your are actually meant to do.
- Get a helicopter - The Annihilator and Buzzard can reach the maximum altitude.
- Get to the maximum altititude - Keep flying up until you can't fly up any more.
- Hover over the water.
- Making Sure You Have Your Parachute Equipped, jump out.
- Keep freefalling, and before you hit the water, deploy your parachute.
- Achievement Unlocked - 25G - Adrenaline Junkie.