Second Extinction

Load up an expedition, and select Lata Plains. Once dropped into spawn area, head towards your right. You'll see a hot springs water area, and a bridge to your left. Run under the bridge and jump off the cliff. Hold the give up button, rinse and repeat. Dying this way took about 30 seconds total. Happy achievement hunting everyone! This method also works for Can't touch me(40 respawns) and Unstoppable force (100 respawns)!

If you don't get this naturally by playing with a friend. Load up a game of insane (any difficulty works, just faster to go down on insane difficulty).

Have your friend stay somewhere safe, while you find dinos and keep going down, hold to bleed out. and then you have a choice to respawn. Dying near a camp where you baited dinosaurs makes this quicker if you keep respawning there. Takes roughly a minute to respawn in between the respawn timer and spawn selection, as well as the drop pod.

Repeat 20 times and it should pop