Lolo Jones Explodes On Tamar Braxton ... 'Bitch, I'm Right Here'

Lolo Jones and Tamar Braxton came thiiis close to throwing hands in the "Celebrity Big Brother" house ... after the Olympian called Tamar a "bitch" during a heated confrontation.

Tensions had been building between the two houseguests for days -- but things finally "popped off" Saturday morning when an argument exploded into real smack talk ... and threats of physical violence.

Tamar -- wearing a weird "Back to the Future" mask -- did NOT back down from Lolo ... telling her, "I am from Baltimore. You do not want that problem."

When Tamar got into Lolo's face, Jones flexed on Tamar and said, "I'm right here."

In a moment captured on the 'Big Brother' live feed -- you can see Tamar saying, "The…