When someone behaves in a way that makes you not want to have any association with that person, that person may as well be dead to you.
Example

Person 1: yo brah have you heard that Bill is now dating a 16y/o
person 2: that's legal but he's 29 isn't he?
person 1: yeah haha he's on a dead man ting nowadays
by kanye wong August 11, 2015
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