National Gorilla Suit Day, everyone. Invented by Mad magazine's Don Martin in 1963, it's evolved into a way to celebrate the late Martin's goofy genius thanks to the efforts of writer and blogger Mark Evanier. (Find out a little more history of the holiday on this page.) Be sure to send gifts and well-wishings to any apes, baboons, or monkeys of your acquaintance. I'm not sure what kind of gift is appropriate, but a bouquet of bananas probably would hit the spot.
Related: The Don Martin Dictionary, collecting hundreds of the bizarre sound effects that made his cartoons so memorable—everything from the dentistry-related "AAAAGH! EEEEEOOOW ACK! UGH UGH MMP AGH! AEEK" to "ZZZZ ZZZZ ZZZZ ZGLUK," which is of course what it sounds like when somebody sleeping has a fish tossed down his throat.