Someone gives you news that may be absolutely right; perfectly true, but is not good news. (thus should not be celebrated with the standard "right on")
To be right off on something means that you're addiction has taken control of the wheel and is what is driving your actions. Someone who is right off on pills will spend all their money and time just trying to get more pills.
It's the point in time when you go from functioning addict to full blown addict. People who are right off usually lose their job, relationships, apartments, car and anything else of value.
There's absolutely no chance I'm hell I'm letting her babysit when she's right off on the shadies. She'd no doubt try to sell my tv or my kid for a fix.
Similar to right off the bat, right off the smack refers to the first thing that is necessary, done, or noticed. The modification of this phrase is used to ground the jargon to just getting off the effect of heroin, smack, which impairs cognitive function.