A person who has smoked crack cocaine for many years, decades even. So much that they have made it a career to smoke rock. They are experts in the field of crack smoking.
That man who smoked crack for 20 years is so experienced that he's a crackologist.
Crackology is the science of everything to do with crack. This includes but is not limited to; smoking, cooking, selling, and bargaining for crack cocaine. Sometimes referred to as a Crackologist.