Guinea pigging

A sexual act where you insert your whole arm up the anus of a man/women. Blood is the only lubricant involved. This act usually involves rolling up the sleeves of your shirt. It is also known by a certain cloud of gathers as a NB.
Friend 1 : Yeah, I was Guinea Pigging my wife last night.

Friend 2 : Oh yeah your wife is loose!
by Bruntwins June 20, 2011
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