To crack onto someone is an Australian phrase meaning to hit on someone, or make a move on someone.
"I was at the club last night and this jackass just came up and started cracking onto me, so I shot him four times in the leg"
"Pff, the jerk. He can't just crack onto someone like that"
"I know! Anyway, I called the hospital and they say he'll never walk again"
by Nuckpang February 24, 2008
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