To tell the truth about something.
OR
Slang for hardcore truth or dare, where all dares involve stealing cars, doing drugs (i.e. Cocaine), or capping someone's ass, or curbing them if you're one evil motherf**er.
Damn, he's good at truthing, I told him to steal Pedro's radio, but he took the tires and the gas to.
When used by a conspiranoic morron this terms describes the act of representing himself as a total failure to human reason by vomiting any crazy conspiracy bullshit.