Well, actually, Yale outpranked Harvard with a carefully orchestrated prank at the 2004 edition of The Game in which members of the nonexistent “Harvard Pep Squad” got Harvard fans to hold up cards spelling out an anti-Harvard dig (see below). Mementos of the prank are on sale to defray expenses.

The Yale Daily News has full coverage, including some lines that are either false or a sign that things have really changed since I was a Yale undergraduate:
A “genuine difference” between her high school friends who go to Harvard and those who go to Yale, [a Yale student] said, is that people are just happier at Yale.
Boy, that was not true when I was at Yale: Yale students had to take more courses and do more writing and generally work much harder. The modal student probably learned more, but also suffered more. Plus in those days, New Haven was less salubrious than it is now.
Note: The original version of this prank is The Great Rose Bowl Hoax, which is listed at number one of the Top 10 College Pranks of All Time. Myself, though, I'm partial to MIT Hacks.