def 2) Something being just plain stupid, idiotic or wrong.
2.)OJ trying to get back his memoribilia was the jenkiest idea he's had in a while.
Since the product is considered the poor man's marijuana, jenky (in adverbial form) refers to something or someone of reduced quality standards among a population where better quality standards exist. Thus the term jenky is relative to the subset of the population in reference.
(2) After having eaten home-cooked meals during the summer break, Charlotte initially rejected the jenky cafeteria food her school provided.