Gamer has been removed
Easiest way to get this 'cheevo is to have two controllers and have one sign in with a dummy account. Make a local Warzone match, set the map to Subway, and change the rounds to 3. Using the dummy account's remote, run for the grenades and blow yourself up. If you spawn inside, take a right and go through the train car. If you spawn outside, go down the stairs, take a right, and go through the train car. Have Fun!
~Skater (Edit: Now ~Squidy)