Bobbi Kristina is on a mission to make sure grandma Cissy Houston's new tell-all book crashes and burns -- by BOYCOTTING it altogether and pleading with her fans to do the same.

Cissy released a book this week called "Remembering Whitney" -- which is all about Whitney Houston's life -- and made the rounds on a slew the talk shows promoting the hell out of it.

But Bobbi wasn't too happy, tweeting to her 119,000 plus followers, "Anything concerning my grandmother's book, I and @nickgordon of course personally have nothing to with."

She continues, "I haven't read and won't ... I find it to be disrespectful to my mother and me being her daughter won't tolerate it."

FYI -- Cissy was on Oprah earlier this week (again promoting the book) and admitted her relationship with BK was strained ... and admitted she knew that Bobbi didn't want the book written.

Whitney Houston's brother says HE'S to blame for introducing the singer to drugs like crack cocaine back in the '80s ... not Bobby Brown ... and last night he came clean to Oprah.

Michael Houston sat down with his mother Cissy and spilled his guts to Her Royal O-ness on "Oprah's Next Chapter" ... admitting he was the first person who did drugs with Whitney. 

Michael says he feels extremely guilty for Whitney's death -- but says he didn't realize how deadly drugs could be when he first brought them to Whitney's doorstep ... explaining, "You gotta understand at the time ... the '80s ... it was acceptable."

Houston adds, "It's painful ... I feel responsible for what I let go so far."

Whitney died in Beverly Hills last February after a drug binge that included cocaine, Xanax and marijuana.