Satire of the popular weight loss and diet program "Jenny Craig"; Referring to a diet driven by methamphetamines causing rapid weight loss. Usually referring to a white trash crank addict who has recently lost a lot of weight. Originated in Terre Haute, Indiana.
1st Guy: Damn dude! Did you see Jessica?
2nd Guy: Yeah she got real skinny, yo!
3rd Guy: I heard she's Jenny Crankin It!
1st & 2nd Guy : Ohhhh, that explains it.