The Dick Van Dyke Show (1961)

S1E25 Where You Been, Fassbinder?

Sally realizes she has no one to celebrate her birthday with, but then receives a call from an old high school friend, Leo Fassbinder. Excited, she invites Leo over for a low-key celebration at her apartment. Meanwhile, Rob, Laura, Buddy, and Mel are skeptical about Leo's existence, suspecting he's just an imaginary friend. They decide to throw a raucous party at Sally’s place, completely unaware of her plans for a quiet night with Leo.