O.J. Simpson: I'm Not Khloe's Dad, 'Trust Me'

O.J. Simpson seems pretty convinced he's NOT Khloe Kardashian's real father -- and he's banking on you buying those two magic words ... "Trust me."

Juice finally addressed the conspiracy theory that's been floating around for decades ... that he secretly knocked up Kris behind Robert Kardashian's back 34 years ago -- and the family has been covering it up ever since.

So, when he was out in Vegas over the weekend -- a photog asked if congratulations were in order regarding Khloe's pregnancy.

Simpson clearly understood the subtext -- and replied, "Well, for Bob, God bless his soul, yeah. I don't know for me. I don't think for me I have nothing to do with it."

He added, "I would be proud ... but trust me, I had nothing to do with it."

Meanwhile, watch O.J.'s daughter, Arnelle, in the background -- she's CONVINCED her dad's no Kardashian creator.