Such as a gangster is to a gang, a ganjster is to the ganj.
Simply put, someone who smokes cannabis regularly without allowing the judgemental views and negative connotations associated with smoking marijuana that presides in social conformity to affect his/her own agenda relative to smoking.
Jake - "bro you smoke so much!"
Nilz - "i don't give a fuck bro, i'll smoke as much as i want."
Jake - "You're such a ganjster!"
a jamcian thug! or a gangster that smokes da dro bro!
: Dude look at that a jamacian man! all thugged out!
:yeah dude!, hes a strait up ganjasta!
:is that a knife?...
:ha well if it is he jsut smoked his knife