1974, Dir. Bob Clark
Like this movie, I am Canadian. Unlike this movie, I am not credited by many as starting the "slasher" genre of horror films. (Besides, wasn't that Psycho?) This film has become a cult classic, and even spawned a critically lambasted remake in 2006 (bringing back fellow Canadian and SCTV alumnus Andrea Martin, whom you can see in the clip below, two years before SCTV began.) The 2006 version of Black Christmas does not retain the reference that earns the original a place on this site.
Context: It's Christmastime at a sorority house! The girls don't know that as they make merry inside, someone sinister is climbing the trellis outside into the attic. Soon after this mysterious and (spoiler alert: murderous) stranger arrives, the phone rings downstairs. The caller is identified by one of the girls as "The Moaner", and as the other sisters gather around to listen to his weird noises, one of the more incredulous girls asks if the sounds coming from the phone could possibly be made by only one person. Barb Coard (Margot Kidder) has a snappy answer...
Exegesis: Ah, the Mormon Tabernacle Choir. Their fame is responsible for many of the references on this site. (Like, Fletch for example). Margot Kidder, who would go on to play the iconic Lois Lane in the Superman films, sells the line with her deadpan sarcasm. (You see, the Mormon Tabernacle Choir doesn't really make annual obscene phone calls...)
I recognize that to deconstruct a joke is to destroy it, but I continue to attempt nonetheless. The humour here stems from the dichotomy between the image of the Mormon Tabernacle Choir (which is indeed comprised of more than one person) and the deranged pervert making the phone call.
The Mormon Tabernacle Choir, or "MoTab" as it is called by many Mormons (and perhaps others, I have no idea) is a world-famous choir. They are sponsored by the Church, and as far as I know, comprised solely of Latter-Day Saints, but they are financially self-sufficient, earning money from tours and album sales. (It doesn't hurt that all 360 of its members are volunteers.) You can learn all about them on Wikipedia, or on their very own website.