Early in the film, Rick notes that, with Roman Polański as a neighbor, he's one backyard party away from getting cast in a hot new film. At this point, the audience believes that the Manson Family will eliminate that possibility. In the end, however, Tate and company survive, and Rick gets warmly received by the household, suggesting that he might indeed make friends and earn a big role in a future film.
Cliff's initial calm reaction in face of the house invasion isn't solely due to being high and drunk. Tex is the biggest threat thanks to his gun but Cliff, being a former soldier and current stuntman, would recognize it's not a threat until the hammer is cocked. With Brandy already in position to jump, Cliff's only real concern is whether he's about to attack some idiot with a gun or a hallucination. Made all the more true by the fact that Cliff was very experienced in doing stunts for Westerns, which heavily make use of single-action revolvers such as Tex's. Combined by the fact that, in the establishing shot of Cliff's house, he's shown to own a similar revolver himself, he likely knew exactly how the firearm operated and prepared accordingly.
When Rick confronts Susan, she suddenly spins and aims her revolver directly at him, but he roasts her before she can get her shot off. Rick proves himself just as fast on the trigger as his various gunslinger roles.
Out of respect the movie shows the real Sharon Tate on the screen in The Wrecking Crew. So it can be interpreted as a nice meta-reference that of course the ticket girl and the usher take a while to recognise her, because that's not the real Sharon, it's Margot Robbie playing her.