Thundercrack! (1975)

Take a clichéd Horror-story beginning, a remote Gothic mansion, an insane hostess, a group of strangers (four men, three women and a gorilla) and you pretty much begin to see that this is not meant to be a serious film, but rather a parody of several other (older and better) ones. Social and sexual confusion & misunderstanding guarantees that this odd cast of characters will come together and entertain & amuse.