Cardi B is FUMING over the NYPD allegedly shutting down her pal's back-to-school event -- and speaking of fumes, she wants New York's finest to choke on hers. Also it's just about time for Tekashi 6ix9ine to pay the piper, testifying in open court against his alleged kidnappers ... while knowing full well it could make his family members targets of gang retaliation.