Crack cocaine has a wide range of effects. Some people just get energetic, others become disorganized to the point of extreme dysfunction. To be "on crack" is

Crack cocaine has a wide range of effects. Some people just get energetic, others become disorganized to the point of extreme dysfunction. To be "on crack" is to display any of these qualities; sometimes good, sometimes bad. I usually see it used to describe a positive trait in the form of high energy / confidence.