Bam Margera is sending a clear message to his former "Jackass" costar Johnny Knoxville ... vowing to knock him out in a boxing ring, and he says it's all for revenge.
Bam posted the disturbing invite late Monday night, calling out Johnny and the show's co-creator Jeff Tremaine for, in his words, hooking him on "18 different medications" that he claims messed him up permanently ... and now he wants to get back at him with a little bare knuckle boxing match.
He goes on to taunt Johnny, double-dog daring him to agree to the fight without gloves.