Years ago I was in a revival house watching It came from Outer Space in 3D. Russell Johnson has a small bit part in it and he appears in a scene in a car and the group I was with yelled out it’s the Professor!! Everyone in the theatre laughed.
I remember reading Ed O’Neill (Al Bundy on Married With Children) say that shortly after the show ended he got a serious role in a stage play. But when he walked on stage the first time, the whole audience cracked up laughing. “Al” was too big to overcome - I suspect Russell Johnson and the rest of the Gilligan’s Island crew had the same problem later in their careers.
Same thing happen when a group of us went to see Cliffhangers. Ralph Waite was about to die and someone yelled out Goodnight Daddy.