JuJu Smith-Schuster Says TikTok Collabs W/ Jackson Mahomes 'Not Happening'

Two of the biggest TikTok stars on the planet will NOT join forces to dominate the social media app ... 'cause JuJu Smith-Schuster says a collab with Patrick Mahomes' lil' bro, Jackson is straight-up "not happening." Jackson -- who has 1 MILLION…