the easy way to do this is on zombies single player on five. buy quick revive and try not to die. use pistol 1st 2 rounds.( when killing zombies. use about 3 bullets then stap u will get more points) u need to rack up about 5000 points level 4-5 when u running low on pistol buy single shot rifle, this time put 2 bullets in chest and stab, if u have over 5000 near end of round 4-5 try get a crawler, and make your way down 2 elevators, turn switch on in lab area teleport to pentegon room and turn on all defuon switches when u are at defqon level five, stay up high on platform at watch teleport for thief to come through soon as u see him cook a grenade and blow yourself up, this will put u down with quick riveve but gives u pack a punch pistol akimbo. should be easy to blow him up
i used revive once. but got enough points to buy it back again, collect bomb 1000pts and any other upgrades, these will all help. took me about 3 attempts to get cheevo