Months after Pamela Anderson accused the actor of flashing her on the set of "Home Improvement," Casey has blasted him as "such a bitch" ... claiming working with him was "the truly single worst experience" she's ever had with a costar. Ouch.

She recalls shooting a scene in which her character confuses Santa for an intruder ... saying: "So I'm throwing things at him. [He] goes over to the producer who is standing four feet from me and goes, and I hear him, he goes, 'You gotta tell her to stop stepping on my lines.'"

Casey says that a producer turned to her horrified and relayed the message ... acknowledging that "everybody was walking on eggshells" around the veteran actor.

And that wasn't all ... as Casey claims when he was done "he was so f***ing rude. Never made eye contact, never said anything."

To mark his exit on the show, she says he announced he was leaving to everyone, picked up his Santa cape, dropped it on the floor and walked out -- with crew members scurrying to pick up the velvet cape.

Casey also alleges that a crew member told her she was seeing Tim "on a good day" -- adding one last damning statement: "He's a bitch."