A very sketchy person. One who does sketchy things or acts in a sketchy manner- a sketch.
Coined at Carrboro High School in 2009 by the Quiz Bowl team when a sketchy member brought three small, highly suspect blueberry muffins that potentially contained marijuana. They were later sold to the general public.
That dude came to school high as a kite. What a sketch-muffin.
That couple has been in that janitor's closet for 15 minutes. They are two sketch-muffins.
This man is a sketch-muffin as he has not bathed in three weeks and smells like vomit.