Behind the Screen is a 1916 Chaplin short silent film I discovered as I looked at a list of movies linked from Goat Dog's Movies About Movies blogathon announcement post. There is a review at BFI, with part 1 here continued here.
When she doesn't make it as an actress the actress wanna-be dresses as a man to work in the movies as a stage hand. Chaplin, as a crew member, likes "him" -especially when Chaplin finds out he's a she. When the foreman sees them kissing he thinks they are gay and makes fun of them. There are pratfalls and slapstick and pie fights. You can also learn some helpful information by watching this little film, like not to just stand around on the trap doors.
Other movies I've seen from that list are linked here.