(adj) Hilarious way to describe a person, place, or thing as suspect, questionable, unsafe, dishonest, or disreputable. A play on words that nonsensically incorporates reference to cartoon character, Spongebob Squarepants.
During a night of drinking, the first friend to pass out then becomes a 'sketchbook' for all those in possession of a sharpie. This friend is subsequently photographed and posted to Facebook, thus becoming a Sketchbook Friend.