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3.
some one who does or says sketchy things. overly sketchy, suspicious.
ruby: OMG guess what matt told me last night?
catherine: what?
ruby: he said we should go to the woods at night
catherine: what a sketch monster!
by candycanelegs September 03, 2012
 
1.
Someone who is doing something wrong and is being obvious or looking guilty.
Somone is dealing crack in front of a cop. "look at that sketch monster!"
by carla and tracy October 26, 2007
 
2.
One who is sketchy in monstrous proportions.

One who is very, very suspicious or acts in suspicious ways.
(Random guy hides behind a wall.)
Person 1: Dude, look at that sketchmonster behind that wall.
Person 2: Yeah, seriously. Look at him. Standing behind that wall.
by Pdoany. February 25, 2009