people who are always coming up with ideas of how to get something for nothing, i.e. how to get something out of the store without the alarm going off at the door, always scheming and plotting in criminal types of ways, a slick mofo

the study of crime scenes

When you're genuine on a good day, but display criminal behavior every now and again

Someone who is really shady. Most likely does drugs and has no problem with hurting someone and getting in trouble with the law.

When someone steals you hair straighteners (specifically your sister). It is an adjective.