a. A person that is so involved in drugs, alcohol, sex, and general debauchery above what is conceiveably possible.
b. A shady character.
c. Someone that appears to have no moral judgment, self-respect, or general hygiene to the point where he/she is a total laughingstock that must be avoided.
> Holy crap man, he lives in Roxbury, obviously hes a sketchball.
> She dumped him and went out with two other guys on the same day? Holy sketchball, batman!