Shift Case

A person who exhibits extremely shifty behaviour (IE: Looking around excessively, wearing baggy clothing when it's warm out, sweating, shaking, breathing heavily, etc.). Usually turns out to be either some sort of sex offender, a shoplifter, or both.

"Dude, did you see the Shift case who just left our store? He smelled like... rotting onions. I wonder what he stole?"