When Tex Avery was one of the animation directors at Warner Bros., he turned out some neat stuff (including Bugs Bunny's debut "A Wild Hare"). One of his early ones was "Don't Look Now", in which Cupid and the Devil have their work cut out on Valentine's Day. Cupid goes around making people fall in love, while the Devil undermines relationships by throwing things all over the men so that it looks as if they've been having affairs. So, the two beings keep one-upping each other...until they figure out the most unpredictable negotiation ever.
It's a pretty interesting cartoon. As it is, anything relating to Valentine's Day has a different significance for me as an Oregonian (Oregon became a state on February 14, 1859). And although I know that it's St. Valentine's Day, I've only heard that description in reference to the St. Valentine's Day Massacre; not a very valentine-like event.
Anyway, this cartoon is worth seeing. And also watch Nicolas Roeg's 1973 movie "Don't Look Now", starring Julie Christie and Donald Sutherland. The combination of this cartoon and that movie should give you a whole new impression of the phrase!