Fastest way to do this is have everyone hold a grenade and stand together in the spawn. Then drop your grenade into the group and walk to them so you all die together.
Do this for 3 rounds on each DEFAULT (not dope bag) map and this achievement unlocks.
You can also play normal games, especially here on TA by setting up play sessions ("just for fun" sessions, for example) to cover all the default maps and have some fun fragging each other! It doesn't matter if you win or lose, you just have to play through each session.
It's your choice how you'd like to do it