Lenny Dykstra's son says the MLB star has told him personally he wants to murder Bagel Guy in their fight next month ... telling TMZ Sports, "He told me he's not stopping 'til he's dead!"
The former Phillies star is set to square up with Chris Morgan (that dude who went crazy in a bagel shop earlier this year) in a celeb boxing match on Sept. 28 ... and the trash talk has already been intense.
Dykstra clowned Bagel Guy's penis size to TMZ Sports earlier this month .