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2.
Going missing. Being kidnapped, murdered or just being Missing.
What ever happened to Sean? I haven't seen him in weeks.

Sean was messing with the wrong crew and got milkboxed, nobody knows what happened to him.

Saying comes from the pictures of missing people on the back of milk boxes.
by Westcoast777 March 27, 2011
 
1.
(verb) Causing someone to go missing or kidnapped. (photos of missing people were displayed on milk cartons)
"Put your hands on my girl again and you'll get milk boxed!"
by psquiz July 07, 2008