A person who has taken too many hard drugs and is slipping in and out of reality. Symptoms of 'flakyness' include dropping off to sleep, rolling of the eyes, slumped body language and a refusal to do anything constructive due to drug-enduced full-body shutdown.
Bob - "Jim, your lookin flaky man. How much have you had?"
Jim - "Ugh. Can't remember man. Nah, lowe it. Cba talking"
Jim passes out, slips off his chair and collapses on the floor. He breathes lightly.