1) Bump off 2) Bump off; rub out 3) Cause the demise of 4) Completely exhaust 5) Dispatch 6) Doing 7) Finish off 8) Ice, so to speak 9) Injure gravely 10) Kill 11) Knock off 12) Make tired 13) Murder 14) Neutralize 15) Put away 16) Rub out 17) Rub out, mob-style 18) Ruin 19) Ruin totally 20) Screw over 
doing
(In SMS-language:) doing