Bill Cosby Sues Beverly Johnson ... She's a Liar with a Washed-Up Career

Bill Cosby says one of his key accusers is shamelessly trying to ruin him with bogus sexual assault claims to revive her failing career, and he's now suing her for defamation of character.

Cosby says Beverly Johnson, an iconic model who claimed he drugged and sexually assaulted her during an audition, has gone on a smear campaign ... making claims to Vanity Fair and other media, and he says all she was doing was grasping at straws to become relevant again.

The comedian gets specific in his lawsuit, pointing to Johnson's allegation he committed his misdeeds while they dined alone at his house. Cosby says the only time they had dinner was when Cosby's wife was present ... he never dined with her alone.

Cosby is on the offensive. Last week he sued 7 other accusers, also claiming they defamed him.