Gulp (1976)

While making his lunch break "just one hour" so his office workers won't take advantage, one hour is still enough for Mr. Bigelow's workers. In the privacy of Mr. Bigelow's now abandoned office, the first worker Barbara immediately undresses and lies down on his desk, when her boyfriend comes along and has sex with her on the desk. The African American shoeshine man polishes Mr. Bigelow's boots while having sex with another female worker. In another office, Sylvia masturbates with a celery stalk because her boyfriend Fred from the first office fails to show up. The last female worker, Janet, invites a fellow male worker to have sex on her desk. When he's all done, the still nude Barbara, who peeps on them, reveals herself and gets it on with Janet. Fred later catches them and gets over not seeing Sylvia by accepting the invitation to have a threesome. Meanwhile, it turns out the worried Mr. Bigelow uses the lunch break for sex himself - he eats his lunch at home while having sex with his maid, asking her to repeat the way she used to do it with his father before him.