Make sure your doing it right and the room settings are correct.
Make it old school with max health DOUBLED.
Make health regeneration FAST.
and make it a free for all. Easiest.
Go to your spot on the map. And I'm sure you know how to set it up right? If not, here's how I do.
1) Press Start
2) Go to INVITE FRIENDS
3) Invite someone who is currently in the game
4) An error should pop up, HOLD THE PS button on your controller and TURN OFF CONTROLLER
5) Turn it back on
6) Press O (circle) 360 i think it's X
7) Jump and press select

Have someone shoot you in increments of 3 for 18 times. 5 seconds after each 3 shots.
There you go.