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1.
When a new school year begins, and the older students decide to point the Freshmen (Grade 9's) out.

In ways, by chasing them around school and drawing dicks on their faces.

NOTE:Only Grade 12's can achieve this prank; younger grades should ask the Grade 12's.
Originating in Toronto,Ontario.
Grade 11 :Hey Man, check out that grade 9. He is annoying, why don't you go Niner him for me, please?
Grade 12: Sure, just let me grab a marker and some tape and start Ninering.
*chases freshman*
by elephantPARADE June 21, 2009
 
2.
The act of boasting about your sports team's previous accomplishments when said sports team is faced with defeat and adversity in the current season. Usually done as an act of self-consolation, or when backed into a corner in a debate/argument.

Those guilty of Ninering are often fans of historically successful franchises and cannot deal with losing in a secure and gracious manner, leading to petty gloating.
I commented to Jeff that Colin Kaepernick seems to be struggling against higher quality secondaries this season, and he got snippy and started ninering about one of their 5 Super Bowls from 20 years ago.
by Earl Richards September 30, 2013