You can do this by yourself in a private match.
........Loadout...........
Faction: Survivors
Explosives slot: Frag launcher
Perks: Extra ammo and Explosive resistance (both optional, but helpful).
Map: Monastery (most pitfalls, any game mode goes)
........Method................
When you spawn, switch to Frag launcher and lob the grenade close to your feet (2-3 meters away). Boom! Watch the ragdoll animation. Get up and let your health regen (wait for the blood to vanish from your HUD) before firing the 2nd shot.
Once you've used up both G launcher shots, jump out of bounds or kill yourself by shooting an explosive barrel. Respawn, rinse & repeat.
........Notes................
I wasn't able to survive explosive barrel blasts even with the expl. resistance perk. Don't waste your time.
Refill grenades by looting salvage crates, if you're against dying.