Kill me backwards is a Hawaiian slang for "that's unfortunate" or simply just "fuck"
Some extentions include,
Kill me backwards to china
(when something is probably very bad)
Kill yourself backwards
(when you feel bad for a friend either because they are going through things or simply just because they are unfortunate)
Person: *trips over*
Person: ahg kill me backwards
Person: *gets into a tricky situation *
Person: kill me backwards to china
Person 1: I tried to kill myself yesterday...
Person 2: kill yourself backwards, do you need help?